U.S. patent number 10,322,377 [Application Number 15/120,484] was granted by the patent office on 2019-06-18 for method for increasing the fouling resistance of inorganic membranes by grafting with organic moieties.
This patent grant is currently assigned to Universiteit Antwerpen, Vito NV. The grantee listed for this patent is UNIVERSITEIT ANTWERPEN, VITO NV. Invention is credited to Anita Buekenhoudt, Vera Meynen, Ghulam Mustafa, Kenny Wyns.
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United States Patent |
10,322,377 |
Buekenhoudt , et
al. |
June 18, 2019 |
Method for increasing the fouling resistance of inorganic membranes
by grafting with organic moieties
Abstract
Provided herein are filtration membranes for water treatment,
and methods for preventing fouling of such membranes. The method
described herein comprises grafting the membrane surface with an
organic moiety, by reacting the surface with an organometallic
reagent, a phosphonate, a phosphinate, or an organosilane.
Inventors: |
Buekenhoudt; Anita (Geel,
BE), Wyns; Kenny (Lommel, BE), Mustafa;
Ghulam (Mol, BE), Meynen; Vera (Geel,
BE) |
Applicant: |
Name |
City |
State |
Country |
Type |
VITO NV
UNIVERSITEIT ANTWERPEN |
Mol
Antwerp |
N/A
N/A |
BE
BE |
|
|
Assignee: |
Vito NV (Mol, BE)
Universiteit Antwerpen (Antwerp, BE)
|
Family
ID: |
50150663 |
Appl.
No.: |
15/120,484 |
Filed: |
February 24, 2015 |
PCT
Filed: |
February 24, 2015 |
PCT No.: |
PCT/EP2015/053772 |
371(c)(1),(2),(4) Date: |
August 19, 2016 |
PCT
Pub. No.: |
WO2015/124784 |
PCT
Pub. Date: |
August 27, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170065936 A1 |
Mar 9, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Feb 24, 2014 [EP] |
|
|
14156401 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C02F
1/44 (20130101); B01D 69/148 (20130101); B01D
71/024 (20130101); B01D 65/08 (20130101); B01D
67/0093 (20130101); B01D 67/0079 (20130101); B01D
61/027 (20130101); C02F 1/442 (20130101); B01D
2323/38 (20130101); C02F 1/444 (20130101); C02F
2303/20 (20130101) |
Current International
Class: |
B01D
65/08 (20060101); B01D 69/14 (20060101); B01D
71/02 (20060101); C02F 1/44 (20060101); B01D
61/02 (20060101); B01D 67/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2055226 |
|
May 2009 |
|
EP |
|
WO 2008/112745 |
|
Sep 2008 |
|
WO |
|
WO 2010/106167 |
|
Sep 2010 |
|
WO |
|
Other References
Castro et al., "The permeability behavior of
polyvinylpyrrolidonemodified porous silica membranes," Journal of
Membrane Science, vol. 84, pp. 151-160 (1993). cited by
applicant.
|
Primary Examiner: Barry; Chester T
Attorney, Agent or Firm: Knobbe, Martens, Olson & Bear,
LLP
Claims
What is claimed is:
1. An antifouling treatment method of a hydrophilic membrane
comprising an oxide and/or hydroxide of silicon or a metal,
comprising grafting a surface of the membrane comprising said oxide
and/or hydroxide with an organic moiety R.sup.1 or R.sup.10 by
contacting said surface with an organometallic reagent, a
phosphonate, a phosphinate, or an organosilane to obtain a treated
membrane which is at least in part hydrophilic, wherein R.sup.1 is
selected from the group consisting of C.sub.1-12alkyl,
C.sub.6-10aryl, C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-10cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl; wherein R.sup.7 and R.sup.8 are independently
from each other C.sub.1-4alkylene; n is an integer from 1 to 4; and
R.sup.9 is C.sub.1-4 alkyl; and R.sup.10 is selected from the group
consisting of C.sub.1-8 alkylene, C.sub.6-10arylene,
C.sub.7-16alkylarylene, C.sub.7-16arylalkylene,
--R.sup.11[OR.sup.12].sub.mR.sup.13--, C.sub.3-8cycloalkylene,
C.sub.3-8cycloalkenylene, C.sub.4-10cycloalkylalkylene,
C.sub.4-10cycloalkenylalkylene, C.sub.2-12alkenylene, 3- to
8-membered heterocyclylene, 5- to 10-membered heteroarylene,
heterocyclylC.sub.1-6alkylene, heteroarylC.sub.1-4alkylene and
C.sub.2-12alkynylene; wherein R.sup.11, R.sup.12, and R.sup.13 are
independently from each other C.sub.1-4alkylene, and m is an
integer from 1 to 4; wherein R.sup.1 and R.sup.10 are optionally
substituted with one or more groups independently selected from
hydroxyl, --OR.sup.4, amino, halo, sulfhydryl, --SR.sup.5, --COOH,
and --COOR.sup.6; wherein R.sup.4, R.sup.5, R.sup.6 are
independently selected from C.sub.1-6alkyl, halo and
C.sub.6-10aryl, and wherein the treated membrane has a ratio of
water permeability compared to a same non-treated membrane of at
least 8/20.
2. The method according to claim 1, wherein said membrane comprises
an oxide and/or hydroxide of an element M.sup.1, and said surface
of said membrane is grafted with an organic functional group
R.sup.1, via a direct M.sup.1-R.sup.1 bond; at least one
M.sup.1-O--P--R.sup.1 bond; a M.sup.1-O--Si--R.sup.1 bond; a
M.sup.1-O--P--R.sup.10--P--O-M.sup.1 bond; or a
M.sup.1-O--Si--R.sup.10--Si--O-M.sup.1 bond; wherein M.sup.1 is a
metal or silicon; and R.sup.1 and R.sup.10 have the same meaning as
defined in claim 1.
3. The method according to claim 1, wherein said organometallic
reagent is a compound of the formula R.sup.1-M.sup.2, or of formula
R.sup.1-M.sup.2-X, or of formula R.sup.1-M.sup.2-R.sup.1'; wherein
M.sup.2 is Li or Mg, and X is halo; R.sup.1 has the same meaning as
in claim 1; and R.sup.1' is, the same or different from R.sup.1,
selected from the group consisting of C.sub.1-12alkyl,
C.sub.6-10aryl, C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-10cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl; optionally substituted with one or more groups
independently selected from hydroxyl, --OR.sup.4, amino, halo,
sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6; wherein R.sup.4,
R.sup.5, R.sup.6 are independently selected from C.sub.1-6alkyl,
halo and C.sub.6-10aryl; R.sup.7 and R.sup.8 are independently from
each other C.sub.1-4alkylene; n is an integer from 1 to 4; and
R.sup.9 is C.sub.1-4 alkyl.
4. The method according to claim 1, wherein said phosphonate or
phosphinate is a compound chosen from formula (I) ##STR00008## or a
salt or ester thereof, wherein R.sup.1 has the same meaning as in
claim 1; or formula (III) ##STR00009## or a salt or ester thereof,
wherein R.sup.1 has the same meaning as in claim 1; and R.sup.1'
is, the same or different from R.sup.1, selected from the group
consisting of C.sub.1-12alkyl, C.sub.6-10aryl, C.sub.7-16alkylaryl,
C.sub.7-16arylalkyl, --R.sup.7[OR.sup.8].sub.nR.sup.9,
C.sub.3-8cycloalkyl, C.sub.3-8cycloalkenyl,
C.sub.4-10cycloalkylalkyl, C.sub.4-10cycloalkenylalkyl,
C.sub.2-12alkenyl, 3- to 8-membered heterocyclyl, 5- to 10-membered
heteroaryl, heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl
and C.sub.2-12alkynyl; optionally substituted with one or more
groups independently selected from hydroxyl, --OR.sup.4, amino,
halo, sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6; wherein
R.sup.4, R.sup.5, R.sup.6 are independently selected from
C.sub.1-6alkyl, halo and C.sub.6-10aryl; R.sup.7 and R.sup.8 are
independently from each other C.sub.1-4alkylene; n is an integer
from 1 to 4; and R.sup.9 is C.sub.1-4 alkyl; or formula (IV)
##STR00010## or a salt or ester thereof, wherein R.sup.10 has the
same meaning as in claim 1.
5. The method according to claim 1, wherein R.sup.1 is
C.sub.1-6alkyl, phenyl, or --R.sup.7[OR.sup.8].sub.nR.sup.9;
wherein R.sup.7 and R.sup.8 are independently from each other
C.sub.1-4alkylene; n is an integer from 1 to 4; and R.sup.9 is
C.sub.1-4 alkyl.
6. The method according to claim 1, for protecting said membrane
against fouling when used for water treatment.
7. The method according to claim 1, wherein R.sup.1 is
C.sub.1-6alkyl or phenyl; and R.sup.10 is C.sub.1-6alkylene or
phenylene.
8. A method for the purification of an aqueous composition
comprising the steps of (i) providing a functionalized at least in
part hydrophilic inorganic matrix comprising an oxide and/or
hydroxide of an element M.sup.1, wherein a surface of said
inorganic matrix is grafted with an organic functional group
R.sup.1 or R.sup.10, wherein, M.sup.1 is a metal or silicon;
R.sup.1 is selected from the group consisting of C.sub.1-12alkyl,
C.sub.6-10aryl, C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-10cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl; wherein R.sup.7 and R.sup.8 are independently
from each other C.sub.1-4alkylene; n is an integer from 1 to 4; and
R.sup.9 is C.sub.1-4 alkyl; and R.sup.10 is selected from the group
consisting of C.sub.1-8 alkylene, C.sub.6-10arylene,
C.sub.7-6alkylarylene, C.sub.7-16arylalkylene,
--R.sup.11[OR.sup.12].sub.mR.sup.13--, C.sub.3-8cycloalkylene,
C.sub.3-8cycloalkenylene, C.sub.4-10cycloalkylalkylene,
C.sub.4-10cycloalkenylalkylene, C.sub.2-12alkenylene, 3- to
8-membered heterocyclylene, 5- to 10-membered heteroarylene,
heterocyclylC.sub.1-6alkylene, heteroarylC.sub.1-4alkylene and
C.sub.2-12alkynylene; wherein R.sup.11, R.sup.12, and R.sup.13 are
independently from each other C.sub.1-4alkylene; wherein R.sup.1
and R.sup.10 are optionally substituted with one or more groups
independently selected from hydroxyl, --OR.sup.4, amino, halo,
sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6; wherein R.sup.4,
R.sup.5, R.sup.6 are independently selected from C.sub.1-6alkyl,
halo and C.sub.6-10aryl, and m is an integer from 1 to 4; and
wherein the treated membrane has a ratio of water permeability
compared to a same non-treated membrane of at least 8/20; and (ii)
filtering said aqueous composition with said functionalized
inorganic matrix to obtain a purified aqueous composition.
9. The method according to claim 8, wherein R.sup.1 or R.sup.10 is
grafted on said surface via a direct M.sup.1-R.sup.1 bond; at least
one M.sup.1-O--P--R.sup.1 bond; a M.sup.1-O--Si--R.sup.1 bond; a
M.sup.1-O--P--R.sup.10--P--O-M.sup.1 bond; or a
M.sup.1-O--Si--R.sup.10--Si--O-M.sup.1 bond.
10. The method according to claim 8, wherein, M.sup.1 is selected
from the group consisting of titanium, zirconium, aluminium,
silicon, strontium, yttrium, lanthanum, hafnium, thorium, iron,
manganese, or combinations thereof.
11. The method according to claim 8, wherein the oxide and/or
hydroxide of M.sup.1 is titanium oxide or zirconium oxide.
12. The method according to claim 8, wherein R.sup.1 is
C.sub.1-6alkyl, phenyl, or R.sup.7[OR.sup.8].sub.nR.sup.9;
optionally substituted with one or more groups independently
selected from hydroxyl, --OR.sup.4, amino, halo, sulfhydryl,
--SR.sup.5, --COOH, and --COOR.sup.6; wherein R.sup.4, R.sup.5,
R.sup.6 are independently selected from C.sub.1-6alkyl, halo and
C.sub.6-10aryl; R.sup.7 and R.sup.8 are independently from each
other C.sub.1-4alkylene; and n is an integer from 1 to 4.
13. The method according to claim 8, wherein said functionalized
inorganic matrix is a membrane comprising a support made of
inorganic material coated with at least one separating membrane
layer made of the oxide and/or hydroxide of M.sup.1 at the
surface.
14. The method according to claim 8, for the purification of an
aqueous composition comprising at least 70 wt % water.
15. The method according to claim 13, wherein the membrane is a
porous membrane with an average pore size of 0.5 nm to 200 nm.
16. The method of claim 1, wherein the water permeability is
measured using deionized water in a cross flow system, with a flow
velocity of 2 m/s, and a trans membrane pressure of 5 bar.
17. The method of claim 8, wherein the water permeability is
measured using deionized water in a cross flow system, with a flow
velocity of 2 m/s, and a trans membrane pressure of 5 bar.
Description
FIELD OF THE INVENTION
The present application relates to the field of filtration
membranes, more particularly ceramic membranes for water
purification, and to methods for preventing or diminishing fouling
of such membranes.
BACKGROUND OF THE INVENTION
Availability of clean water is a growing world-wide challenge.
Consequently, development of efficient water purification,
desalination and recycling technologies is an important topic on
the world-wide research agenda.
Membrane filtration is considered a very powerful purification
technology to tackle this problem. The majority of the membranes
used for water filtration have long been polymeric membranes.
However, more recently also ceramic membranes are finding their way
into this field. The main benefits of ceramic membranes are their
high chemical and thermal stability enabling chemical and/or
thermal regeneration and sterilization by aggressive chemicals
and/or hot steam. Moreover, their high mechanical stability enables
high pressure back-flushing. As a consequence, despite their higher
cost, ceramic membranes are becoming an economically feasible
alternative for polymeric membranes in water treatment.
A critical issue in the development of effective membrane processes
(both for polymeric and ceramic membranes) is the decline in system
performance due to membrane fouling. This limits the economic
efficiency of the operation and slows down large scale industrial
applications of membranes especially in case of fouling caused by
the adsorption of dissolved matter onto the membrane surface and/or
into the membrane pores. This type of fouling is considered
irreversible fouling and can generally only be removed by chemical
cleaning.
Membrane fouling can be decreased by optimization of feed
pre-treatment (e.g. via ultrafiltration, microfiltration,
flocculation, ozonation and/or UV oxidation), and regular physical
and chemical cleaning. Additional measures involve a careful
selection of membrane, module design, and operating parameters.
A more sustainable approach is the prevention of the undesired
adsorption processes by membrane-surface modification. Although
poorly understood, it is generally accepted that fouling of
polymeric membranes in water treatment decreases with an increase
in hydrophilicity of the membrane material. Consequently, research
has been performed to increase polymer membrane hydrophilicity by
grafting, plasma or other surface treatment.
Ceramic membranes, and particularly silicon and/or metal oxide and
hydroxide membranes, generally are intrinsically hydrophilic and
consistently show relative low fouling in water treatment.
Nevertheless, also these membranes become less effective over time
due to fouling.
Grafting of ceramic materials with phosphonic acids is known to
result in stable modified metal oxide surfaces (Mutin et al.; J.
Mater. Chem. 2005, 15, 3761). International patent application WO
2010/106167 describes another stable grafting of organic functional
moieties onto the surface of ceramic membranes in order to increase
the membrane hydrophobicity or change its affinity.
SUMMARY OF THE INVENTION
The present inventors surprisingly found that by grafting silicon
or metal oxide and/or hydroxide membranes with certain organic
moieties, the sensitivity of the membranes to fouling decreases
significantly, while maintaining sufficient hydrophilicity.
Thus, provided herein is a method for reducing the sensitivity of a
membrane comprising an oxide and/or hydroxide of silicon or a metal
to fouling and/or protecting a membrane against fouling comprising
grafting the surface of said oxide and/or hydroxide with an organic
moiety R.sup.1 or R.sup.10 by contacting said surface with an
organometallic reagent, a phosphonate, a phosphinate, or an
organosilane.
The method is further characterized in that R.sup.1 is selected
from the group consisting of C.sub.1-12alkyl, C.sub.6-10aryl,
C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-10cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl; wherein R.sup.7 and R.sup.8 are independently
from each other C.sub.1-4alkylene; n is an integer from 1 to 4; and
R.sup.9 is C.sub.1-4 alkyl; and
R.sup.10 is selected from the group consisting of C.sub.1-8
alkylene, C.sub.6-10arylene, C.sub.7-16alkylarylene,
C.sub.7-16arylalkylene, --R.sup.11[OR.sup.12].sub.mR.sup.13--,
C.sub.3-8cycloalkylene, C.sub.3-8cycloalkenylene,
C.sub.4-10cycloalkylalkylene, C.sub.4-10cycloalkenylalkylene,
C.sub.2-12alkenylene, 3- to 8-membered heterocyclylene, 5- to
10-membered heteroarylene, heterocyclylC.sub.1-6alkylene,
heteroarylC.sub.1-4alkylene and C.sub.2-12alkynylene; wherein
R.sup.11, R.sup.12, and R.sup.13 are independently from each other
C.sub.1-4alkylene, and m is an integer from 1 to 4;
wherein R.sup.1 and R.sup.10 are optionally substituted with one or
more groups independently selected from hydroxyl, --OR.sup.4,
amino, halo, sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6;
wherein R.sup.4, R.sup.5, R.sup.6 are independently selected from
C.sub.1-6alkyl, halo and C.sub.6-10aryl.
In particular embodiments, the membrane comprises an oxide and/or
hydroxide of an element M.sup.1, and said surface of said inorganic
matrix is grafted with an organic functional group R.sup.1, via a
direct M.sup.1-R.sup.1 bond; at least one M.sup.1-O--P--R.sup.1
bond; a M.sup.1-O--Si--R.sup.1 bond; a
M.sup.1-O--P--R.sup.10--P--O-M.sup.1 bond; or a
M.sup.1-O--Si--R.sup.10--Si--O-M.sup.1 bond; wherein M.sup.1 is a
metal or silicon; and R.sup.1 and R.sup.10 have the same meaning as
defined above.
In certain embodiments, the organometallic reagent is a compound of
the formula R.sup.1-M.sup.2, or of formula R.sup.1-M.sup.2-X, or of
formula R.sup.1-M.sup.2-R.sup.1'; wherein M.sup.2 is Li or Mg, and
X is halo; R.sup.1 has the same meaning as defined above; and
R.sup.1' is, the same or different from R.sup.1, selected from the
group consisting of C.sub.1-12alkyl, C.sub.6-10aryl,
C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-10cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl; optionally substituted with one or more groups
independently selected from hydroxyl, --OR.sup.4, amino, halo,
sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6; wherein R.sup.4,
R.sup.5, R.sup.6 are independently selected from C.sub.1-6alkyl,
halo and C.sub.6-10aryl; R.sup.7 and R.sup.8 are independently from
each other C.sub.1-4alkylene; n is an integer from 1 to 4; and
R.sup.9 is C.sub.1-4 alkyl.
In particular embodiments, the phosphonate or phosphinate is a
compound chosen from formula (I)
##STR00001## or a salt or ester thereof, wherein R.sup.1 has the
same meaning as defined above; or formula (III)
##STR00002## or a salt or ester thereof, wherein R.sup.1 has the
same meaning as defined above; and R.sup.1' is, the same or
different from R.sup.1, selected from the group consisting of
C.sub.1-12alkyl, C.sub.6-10aryl, C.sub.7-16alkylaryl,
C.sub.7-16arylalkyl, --R.sup.7[OR.sup.8].sub.nR.sup.9,
C.sub.3-8cycloalkyl, C.sub.3-8cycloalkenyl,
C.sub.4-10cycloalkylalkyl, C.sub.4-10cycloalkenylalkyl,
C.sub.2-12alkenyl, 3- to 8-membered heterocyclyl, 5- to 10-membered
heteroaryl, heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl
and C.sub.2-12alkynyl; optionally substituted with one or more
groups independently selected from hydroxyl, --OR.sup.4, amino,
halo, sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6; wherein
R.sup.4, R.sup.5, R.sup.6 are independently selected from
C.sub.1-6alkyl, halo and C.sub.6-10aryl; R.sup.7 and R.sup.8 are
independently from each other C.sub.1-4alkylene; n is an integer
from 1 to 4; and R.sup.9 is C.sub.1-4 alkyl; or formula (IV)
##STR00003## or a salt or ester thereof, wherein R.sup.10 has the
same meaning as defined above.
In certain embodiments, R.sup.1 is C.sub.1-6alkyl, phenyl, or
--R.sup.7[OR.sup.8].sub.nR.sup.9; wherein R.sup.7 and R.sup.8 are
independently from each other C.sub.1-4alkylene; n is an integer
from 1 to 4; and R.sup.9 is C.sub.1-4 alkyl.
In particular embodiments, the membrane is a water treatment
membrane. In certain embodiments, the method is for protecting the
membrane from fouling when used for water treatment.
In certain embodiments, R.sup.1 is C.sub.1-6alkyl or phenyl; and
R.sup.10 is C.sub.1-6alkylene or phenylene.
The membranes described herein are particularly suitable and stable
for use in filtration in that the grafting with one or more organic
moieties prevents or significantly reduces fouling of the
membranes, compared to the non-grafted filtration membranes. The
hydrophilicity of the grafted membranes is nevertheless still
sufficient to allow an effective use of the membranes for water
filtration. Moreover, the grafted membranes are typically easier to
clean, compared to the non-grafted membranes. Thus, the membranes
are particularly suitable for use in water filtration.
Accordingly, the application further provides the use of a
functionalized inorganic matrix comprising an oxide and/or
hydroxide of an element M.sup.1 for water treatment or water
purification, characterized in that the surface of said inorganic
matrix is grafted with an organic functional group R.sup.1 or
R.sup.10, wherein, M.sup.1 is a metal or silicon; R.sup.1 is
selected from the group consisting of C.sub.1-12alkyl,
C.sub.6-10aryl, C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-10cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl; wherein R.sup.7 and R.sup.8 are independently
from each other C.sub.1-4alkylene; n is an integer from 1 to 4; and
R.sup.9 is C.sub.1-4 alkyl; and R.sup.10 is selected from the group
consisting of C.sub.1-8 alkylene, C.sub.6-10arylene,
C.sub.7-16alkylarylene, C.sub.7-16arylalkylene,
--R.sup.11[OR.sup.12].sub.mR.sup.13--, C.sub.3-8cycloalkylene,
C.sub.3-8cycloalkenylene, C.sub.4-10cycloalkylalkylene,
C.sub.4-10cycloalkenylalkylene, C.sub.2-12alkenylene, 3- to
8-membered heterocyclylene, 5- to 10-membered heteroarylene,
heterocyclylC.sub.1-6alkylene, heteroarylC.sub.1-4alkylene and
C.sub.2-12alkynylene; wherein R.sup.11, R.sup.12, and R.sup.13 are
independently from each other C.sub.1-4alkylene; wherein R.sup.1
and R.sup.10 are optionally substituted with one or more groups
independently selected from hydroxyl, --OR.sup.4, amino, halo,
sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6; wherein R.sup.4,
R.sup.5, R.sup.6 are independently selected from C.sub.1-6alkyl,
halo and C.sub.6-10aryl, and m is an integer from 1 to 4.
In certain embodiments of the present use, R.sup.1 or R.sup.10 is
grafted on said surface via a direct M.sup.1-R.sup.1 bond; at least
one M.sup.1-O--P--R.sup.1 bond; a M.sup.1-O--Si--R.sup.1 bond; a
M.sup.1-O--P--R.sup.10--P--O-M.sup.1 bond; or a
M.sup.1-O--Si--R.sup.10--Si--O-M.sup.1 bond.
In particular embodiments of the use, M.sup.1 is selected from the
group consisting of titanium, zirconium, aluminium, silicon,
strontium, yttrium, lanthanum, hafnium, thorium, iron, manganese,
or combinations thereof.
In certain embodiments of the use, the oxide and/or hydroxide of
M.sup.1 is titanium oxide or zirconium oxide.
In particular embodiments of the use, R.sup.1 is C.sub.1-6alkyl,
phenyl, or --R.sup.7[OR.sup.8].sub.nR.sup.9; optionally substituted
with one or more groups independently selected from hydroxyl,
--OR.sup.4, amino, halo, sulfhydryl, --SR.sup.5, --COOH, and
--COOR.sup.6; wherein R.sup.4, R.sup.5, R.sup.6 are independently
selected from C.sub.1-6alkyl, halo and C.sub.6-10aryl; R.sup.7 and
R.sup.8 are independently from each other C.sub.1-4alkylene; and n
is an integer from 1 to 4.
In particular embodiments of the use, the functionalized inorganic
matrix is a membrane comprising a support made of inorganic
material coated with at least one separating membrane layer made of
the oxide and/or hydroxide of M.sup.1 at the surface.
In certain embodiments of the use, the oxide and/or hydroxide of
M.sup.1 is provided as particles in a mixed matrix membrane.
In certain embodiments, the membranes are porous with an average
pore size of 0.5 nm to 200 nm.
The above and other characteristics, features and advantages of the
concepts described herein will become apparent from the following
detailed description, which illustrates, by way of example, the
claimed methods and uses herein.
BRIEF DESCRIPTION OF THE DRAWINGS
The following description of the figures of specific embodiments is
merely exemplary in nature and is not intended to limit the present
teachings, their application or uses. Throughout the drawings,
corresponding reference numerals indicate like or corresponding
parts and features.
FIG. 1A: Graph illustrating the fouling tendency of grafted and
native titania NF membranes using humic acid (HA) as a model
foulant, in a concentration of 10 mg/L in combination with a
Ca.sup.2+ concentration of 1, 2 and 4 mmol/L at two pH levels.
B: Graph illustrating the fouling tendency of grafted and native
titania NF membranes using laminarin gum as a model foulant, in
concentrations 0.1, 0.25 and 0.5 mg/L.
C: Graph illustrating the fouling tendency of grafted and native
titania NF membranes using meat peptone as a model foulant, in
concentrations 5, 15 and 25 mg/L.
D: Graph illustrating the fouling tendency of grafted and native
titania NF membranes using wood extracts as a model foulant.
FIG. 2: Graph illustrating the reverse osmosis water (ROW) flux
through a membrane before fouling, the foulant solution flux and
the ROW flux after fouling. Horizontal hatching: foulant solution
flux. Italic hatching: ROW flux before fouling. Vertical hatching:
ROW flux after fouling.
DETAILED DESCRIPTION OF THE INVENTION
While potentially serving as a guide for understanding, any
reference signs in the claims shall not be construed as limiting
the scope thereof.
As used herein, the singular forms "a", "an", and "the" include
both singular and plural referents unless the context clearly
dictates otherwise.
The terms "comprising", "comprises" and "comprised of" as used
herein are synonymous with "including", "includes" or "containing",
"contains", and are inclusive or open-ended and do not exclude
additional, non-recited members, elements or method steps. The
terms "comprising", "comprises" and "comprised of" when referring
to recited components, elements or method steps also include
embodiments which "consist of" said recited components, elements or
method steps.
Furthermore, the terms first, second, third and the like in the
description and in the claims, are used for distinguishing between
similar elements and not necessarily for describing a sequential or
chronological order, unless specified. It is to be understood that
the terms so used are interchangeable under appropriate
circumstances and that the embodiments described herein are capable
of operation in other sequences than described or illustrated
herein.
The values as used herein when referring to a measurable value such
as a parameter, an amount, a temporal duration, and the like, is
meant to encompass variations of +/-10% or less, preferably +/-5%
or less, more preferably +/-1% or less, and still more preferably
+/-0.1% or less of and from the specified value, insofar such
variations are appropriate to ensure one or more of the technical
effects envisaged herein. It is to be understood that each value as
used herein is itself also specifically, and preferably,
disclosed.
The recitation of numerical ranges by endpoints includes all
numbers and fractions subsumed within the respective ranges, as
well as the recited endpoints.
Reference throughout this specification to "one embodiment" or "an
embodiment" means that a particular feature, structure or
characteristic described in connection with the embodiment is
included in at least one embodiment envisaged herein. Thus,
appearances of the phrases "in one embodiment" or "in an
embodiment" in various places throughout this specification are not
necessarily all referring to the same embodiment, but may.
Furthermore, the particular features, structures or characteristics
may be combined in any suitable manner, as would be apparent to a
person skilled in the art from this disclosure, in one or more
embodiments. Furthermore, while some embodiments described herein
include some but not other features included in other embodiments,
combinations of features of different embodiments are also
envisaged herein, and form different embodiments, as would be
understood by those in the art. For example, in the appended
claims, any of the features of the claimed embodiments can be used
in any combination.
All documents cited in the present specification are hereby
incorporated by reference in their entirety.
Unless otherwise defined, all terms used in disclosing the concepts
described herein, including technical and scientific terms, have
the meaning as commonly understood by one of ordinary skill in the
art. By means of further guidance, definitions for the terms used
in the description are included to better appreciate the teaching
of the present disclosure. The terms or definitions used herein are
provided solely to aid in the understanding of the teachings
provided herein.
In a first aspect, the present application provides a method for
protecting a membrane comprising an oxide and/or hydroxide of
silicon or a metal against fouling.
The term "fouling" as used herein refers to the blocking and/or
plugging of membrane pores during a filtration process, in a way
that degrades the membrane's performance, e.g. by a severe decline
of the flux. The term fouling as used herein includes irreversible
fouling due to organic foulants such as humics, oils, and/or
polyelectrolytes. The term "irreversible fouling" refers to the
strong attachment of foulants, which cannot be removed by physical
cleaning.
More specifically, the present application provides a method for
reducing the sensitivity of a membrane comprising an oxide and/or
hydroxide of silicon or a metal to fouling, in particular
irreversible fouling.
In particular embodiments, the present method allows for reducing
the irreversible fouling of an inorganic membrane by at least 30%,
compared to the membrane prior to grafting with R.sup.1 as
described herein, preferably a least 50%. The amount of
irreversible fouling can be measured by calculating the decline of
the water flux under normal filtration conditions, after fouling
(without chemical cleaning) (see e.g. FIG. 2).
The present method for protecting a membrane against fouling
comprises grafting the surface of the oxide and/or hydroxide with
an organic moiety. The expression "surface" as used herein is
understood to comprise the (macroscopic) outer surface as well as
the inner pore surfaces of a matrix. The surface to which an
organic functional group is adhered may thus be an external surface
and/or an internal surface of the matrix.
The resulting membranes are significantly less sensitive to
fouling, and may be used for the treatment or filtration of various
compositions, including but not limited to aqueous
compositions.
The methods envisaged herein are particularly suitable for
protecting membranes used in water treatment or purification
against fouling. Indeed it has been found that grafting the surface
of an oxide and/or hydroxide with an organic moiety ensures that
the membranes are significantly less sensitive to typical foulants
of water. Thus, the membranes described herein are of particular
interest for the treatment or purification of aqueous compositions.
Accordingly, in a further aspect, the present application provides
in the use of a functionalized inorganic matrix comprising an oxide
and/or hydroxide of a metal and/or silicon for water treatment,
characterized in that the surface of said inorganic matrix is
grafted with an organic functional group, more particularly the
organic functional groups envisaged herein and defined as R.sup.1
or R.sup.10. Optionally, the inorganic matrix may further be
grafted with an organic functional group R.sup.1'. In certain
embodiments however, the inorganic matrix is not grafted with an
organic functional group other than R.sup.1 and/or R.sup.10.
The method envisaged herein involves modification or
functionalization of a matrix. The terms "modification" and
"functionalization" are used interchangeably herein and both refer
to the covalent bonding of organic group(s), also defined herein as
R.sup.1 or R.sup.10, or in particular embodiments R.sup.1 and/or
R.sup.1' moieties, onto a surface of a matrix as defined herein. As
will be detailed below, the covalent bonding of a group R.sup.1 to
a matrix, which is an oxide or hydroxide of a metal M.sup.1, may be
direct (via a M.sup.1-C bond) or indirect (via a M.sup.1-O--P--C or
M.sup.1-O--Si--C bond). In this context the terms "modified" or
"surface-modified" or "functionalized" matrix should also be
considered as synonyms and refer to a matrix as defined herein,
having organic compound(s) attached to their surface, including the
surface of the pores within the matrix where applicable, via
covalent binding.
The inventors have found that to obtain an optimal flux and
antifouling properties, the functional groups R.sup.1, R.sup.1',
and/or R.sup.10 are preferably not too bulky. Indeed, the inventors
have observed that optimal anti-fouling properties are obtained
when R.sup.1 is a group such as methyl or phenyl. It has however
been found that this anti-foulant property can similarly be
obtained with organic moieties the organic moiety R.sup.1 and
R.sup.10 as defined herein below. In particular embodiments,
R.sup.1 and (if present) R.sup.1' are independently selected from
the list consisting of C.sub.1-12alkyl, C.sub.6-10aryl,
C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-18cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl;
wherein R.sup.7 and R.sup.8 are independently from each other
C.sub.1-4alkylene; n is an integer from 1 to 4; and R.sup.9 is
C.sub.1-4 alkyl.
In certain embodiments, R.sup.10 is selected from the group
consisting of C.sub.1-8alkylene, C.sub.6-10arylene,
C.sub.7-16alkylarylene, C.sub.7-16arylalkylene,
--R.sup.11[OR.sup.12].sub.mR.sup.13--, C.sub.3-8cycloalkylene,
C.sub.3-8cycloalkenylene, C.sub.4-10cycloalkylalkylene,
C.sub.4-10cycloalkenylalkylene, C.sub.2-12alkenylene, 3- to
8-membered heterocyclylene, 5- to 10-membered heteroarylene,
heterocyclylC.sub.1-6alkylene, heteroarylC.sub.1-4alkylene and
C.sub.2-12alkynylene; wherein R.sup.11, R.sup.12 and R.sup.13 are
independently from each other C.sub.1-4alkylene;
As indicated above, in certain embodiments, the inorganic matrix
may further be grafted with an organic functional group R.sup.1'.
It is envisaged that R.sup.1', if present, is an organic moiety
independently selected from the list consisting of C.sub.1-12alkyl,
C.sub.6-10aryl, C.sub.7-16alkylaryl, C.sub.7-16arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-8cycloalkyl,
C.sub.3-8cycloalkenyl, C.sub.4-10cycloalkylalkyl,
C.sub.4-10cycloalkenylalkyl, C.sub.2-12alkenyl, 3- to 8-membered
heterocyclyl, 5- to 10-membered heteroaryl,
heterocyclylC.sub.1-6alkyl, heteroarylC.sub.1-4alkyl and
C.sub.2-12alkynyl;
In the embodiments envisaged herein, R.sup.1, R.sup.1' (if
present), and R.sup.10 are optionally substituted. The term
"substituted" is used in the context of the methods described
herein, to indicate that one or more hydrogens on the moiety
indicated in the expression using "substituted" is replaced with a
selection from the indicated group, provided that the indicated
atom's normal valency is not exceeded, and that the substitution
results in a chemically stable compound, i.e. a compound that is
sufficiently robust to survive isolation to a useful degree of
purity from a reaction mixture.
More particularly, as envisaged herein, R.sup.1, R.sup.1' (if
present), and R.sup.10 are optionally substituted with one or more
groups independently selected from hydroxyl, --OR.sup.4, amino,
halo, sulfhydryl, --SR.sup.5, --COOH, and --COOR.sup.6; wherein
R.sup.4, R.sup.5, R.sup.6 are independently selected from
C.sub.1-6alkyl, halo and C.sub.6-10aryl, and m is an integer from 1
to 4.
In particular embodiments, R.sup.1 is C.sub.1-12alkyl. In further
embodiments, R.sup.1 is C.sub.1-8alkyl, more particularly
C.sub.1-6alkyl. In yet further embodiments, R.sup.1 is
C.sub.1-4alkyl. The term "alkyl" by itself or as part of another
substituent, refers to a straight or branched saturated hydrocarbon
group joined by single carbon-carbon bonds. When a subscript is
used herein following a carbon atom, the subscript refers to the
number of carbon atoms that the named group may contain. Thus, for
example, "C.sub.1-4alkyl" means an alkyl of one to four carbon
atoms. Examples of C.sub.1-4alkyl groups are methyl, ethyl, propyl,
isopropyl, butyl, isobutyl and tert-butyl.
In particular embodiments, R.sup.1 is an ether or oligoether of
formula --R.sup.7[OR.sup.8].sub.nR.sup.9, wherein R.sup.7 and
R.sup.8 are independently from each other C.sub.1-4alkylene; n is
an integer from 1 to 4; and R.sup.9 is C.sub.1-4 alkyl. The bond to
the parent moiety is through R.sup.7. In further embodiments,
R.sup.7 and R.sup.8 are independently from each other
C.sub.1-3alkylene; n is an integer from 1 to 3; and R.sup.9 is
C.sub.1-3 alkyl.
As used herein, the term "C.sub.1-xalkylene", by itself or as part
of another substituent, refers to C.sub.1-xalkyl groups that are
divalent, i.e., with two single bonds for attachment to two other
groups. Alkylene groups may be linear or branched and may be
substituted as indicated herein.
In a particular embodiment, R.sup.1 is C.sub.3-8cycloalkyl. As used
herein, the term "C.sub.3-8cycloalkyl", by itself or as part of
another substituent, refers to a saturated cyclic alkyl group
containing from about 3 to about 8 carbon atoms. Examples of
C.sub.3-8cycloalkyl include cyclopropyl, cyclobutyl, cyclopentyl,
or cyclohexyl, cycloheptyl and cyclooctyl. In particular
embodiments, R.sup.1 may be a cycloalkyl selected from the group
consisting of cyclopropyl, cyclobutyl, cyclopentyl, and
cyclohexyl.
In a particular embodiment, R.sup.1 is C.sub.3-8cycloalkenyl. As
used herein, the term "cycloalkenyl" by itself or as part of
another substituent, refers to a non-aromatic mono- or multicyclic
ring system comprising about 3 to 8 carbon atoms, preferably about
5 to 8 carbon atoms, which contains at least one carbon-carbon
double bond. Preferred cycloalkenyl rings contain 5 or 6 ring
atoms, such as cyclopentenyl and cyclohexenyl.
In a particular embodiment, R.sup.1 is a C.sub.6-10aryl. As used
herein, the term "C.sub.6-10aryl", by itself or as part of another
substituent, refers to a polyunsaturated, aromatic hydrocarbyl
group having a single ring (i.e. phenyl) or multiple aromatic rings
fused together (e.g. naphthalene), or linked covalently, typically
containing 6 to 10 carbon atoms; wherein at least one ring is
aromatic. Aryl rings may be unsubstituted or substituted with from
1 to 4 substituents on the ring. Examples of C.sub.6-10aryl include
phenyl, naphthyl, indanyl, or 1,2,3,4-tetrahydro-naphthyl.
In a particular embodiment, R.sup.1 is C.sub.2-12alkenyl,
preferably C.sub.2-6alkenyl. The term "alkenyl" by itself or as
part of another substituent, refers to an unsaturated hydrocarbyl
group, which may be linear, or branched, comprising one or more
carbon-carbon double bonds. When a subscript is used herein
following a carbon atom, the subscript refers to the number of
carbon atoms that the named group may contain. Thus, for example,
"C.sub.2-6alkenyl" means an alkenyl of two to six carbon atoms.
Non-limiting examples of C.sub.2-6alkenyl groups include ethenyl,
2-propenyl, 2-butenyl, 3-butenyl, 2-pentenyl and its chain isomers,
2-hexenyl and its chain isomers, 2,4-pentadienyl and the like.
In a particular embodiment, R.sup.1 is C.sub.2-12alkynyl,
preferably C.sub.2-6alkynyl. The term "alkynyl" by itself or as
part of another substituent, refers to an unsaturated hydrocarbyl
group, which may be linear, or branched, comprising one or more
carbon-carbon triple bonds. When a subscript is used herein
following a carbon atom, the subscript refers to the number of
carbon atoms that the named group may contain. Thus, for example,
"C.sub.2-6alkynyl" means an alkynyl of two to six carbon atoms. Non
limiting examples of C.sub.2-6alkynyl groups include ethynyl,
2-propynyl, 2-butynyl, 3-butynyl, 2-pentynyl and its chain isomers,
2-hexynyl and its chain isomers and the like.
In a particular embodiment, R.sup.1 is heterocyclyl, preferably a
3- to 8-membered heterocyclyl. The terms "heterocyclyl" or
"heterocyclo" as a group or part of a group, refer to non-aromatic,
fully saturated or partially unsaturated cyclic groups (for
example, 3 to 7 member monocyclic, 7 to 11 member bicyclic, or
containing a total of 3 to 10 ring atoms) which have at least one
heteroatom in at least one carbon atom-containing ring. Each ring
of the heterocyclic group containing a heteroatom may have 1, 2, 3
or 4 heteroatoms selected N, O and/or S, where the N and S, where
the N and S heteroatoms may be oxidized and the N heteroatoms may
be quaternized. The heterocyclic group may be attached at any
heteroatom or carbon atom of the ring or ring system, where valence
allows. The rings of multi-ring heterocycles may be fused, bridged
and/or joined through one or more spiro atoms. A "substituted
heterocyclyl" refers to a heterocyclyl group having one or more
substituent(s) (for example 1, 2 or 3 substituent(s), or 1 to 2
substituent(s)), at any available point of attachment. Non limiting
exemplary heterocyclic groups include oxiranyl, pyrrolidinyl,
tetrahydrofuranyl, tetrahydrothiophenyl, dihydropyrrolyl,
dihydrofuranyl, imidazolidinyl, pyrazolidinyl, imidazolinyl,
pyrazolinyl, oxazolidinyl, isoxazolidinyl, oxazolinyl,
isoxazolinyl, thiazolidinyl, isothiazolidinyl, thiazolinyl,
piperidyl, tetrahydropyranyl, indolinyl, piperazinyl, 3-dioxolanyl,
1,4-dioxanyl, 1,3-dioxolanyl, and 1,4-oxathianyl.
In particular embodiments, R.sup.1 is heteroaryl. The term
"heteroaryl", as used herein, represents a stable 5- to 10-membered
aromatic ring system which consists of carbon atoms and from one to
four heteroatoms selected from the group consisting of N, O and S,
and wherein the nitrogen and sulfur heteroatoms may optionally be
oxidized, and the nitrogen heteroatom may optionally be
quaternized. Preferably, said heteroaryl is a 5- to 6-membered
aromatic ring. Examples of such heteroaryl groups include, but are
not limited to, furan, furazan, imidazole, isothiazole, isoxazole,
oxadiazole, oxazole, pyrazine, pyrazole, pyridazine, pyridine,
pyrimidine, pyrrole, tetrazole, thiadiazole, thiazole, thiophene,
triazine, triazole, and N-oxides thereof. Preferably said
heteroaryl is furan.
The term "C.sub.7-16aralkyl" or "C.sub.7-16arylalkyl", as a group
or part of a group, means an arylalkyl in which the aryl and alkyl
are as previously described, wherein the aryl and alkyl together
contain 7 to 16 carbon atoms. The bond to the parent moiety is
through the alkyl. Examples of C.sub.7-16aralkyl radicals include
benzyl, phenethyl, 3-(2-naphthyl)-butyl, and the like.
The term "C.sub.7-16alkylaryl", as a group or part of a group,
means an alkyl-aryl in which the aryl and alkyl are as previously
described, wherein the aryl and alkyl together contain 7 to 16
carbon atoms. The bond to the parent moiety is through the aryl. A
non-limiting example of a C.sub.7-16alkylaryl is tolyl.
In particular embodiments, R.sup.1 is heterocyclylC.sub.1-6alkyl.
The term "heterocyclylC.sub.1-6alkyl", as a group or part of a
group, means a C.sub.1-6alkyl as defined herein, wherein at least
one hydrogen atom is replaced by at least one heterocyclyl as
defined herein, more particularly a 3- to 8-membered heterocyclyl,
more particularly a 3- to 6-membered heterocyclyl, and even more
particularly a 3- to 5-membered heterocyclyl.
In particular embodiments, R.sup.1 is heteroarylC.sub.1-alkyl. The
term "heteroarylC.sub.1-6alkyl", as a group or part of a group,
means a C.sub.1-6alkyl as defined herein, wherein at least one
hydrogen atom is replaced by at least one heteroaryl as defined
herein, more particularly a 5- to 10-membered heteroaryl, more
particularly a 5- to 6-membered heteroaryl. The bond to the parent
moiety is through the alkyl.
In particular embodiments, R.sup.1 is C.sub.4-18cycloalkylalkyl,
more particularly C.sub.4-8cycloalkylalkyl. The term
"C.sub.4-18cycloalkylalkyl" as a group or part of a group, means an
cycloalkyl-alkyl in which the cycloalkyl and alkyl are as
previously described, wherein the cycloalkyl and alkyl together
contain 4 to 10 carbon atoms. The bond to the parent moiety is
through the alkyl. Examples of C.sub.4-10cycloalkylalkyl radicals
include cyclopropylmethyl, cyclopropylethyl, cyclopropylpropyl,
cyclopentylmethyl, cyclopentylethyl, cyclopentylpropyl,
cyclohexylmethyl, cyclohexylethyl, and cyclohexylpropyl.
In a particular embodiment, R.sup.1 is C.sub.4-10cycloalkenylalkyl.
As used herein, the term "C.sub.4-10cycloalkenylalkyl" as a group
or part of a group, means an cycloalkenyl-alkyl in which the
cycloalkenyl and alkyl are as defined herein, wherein the
cycloalkenyl and alkyl together contain 4 to 10 carbon atoms. The
bond to the parent moiety is through the alkyl.
In particular embodiments, R.sup.10 is C.sub.1-8alkylene. In
further embodiments, R.sup.10 is C.sub.1-6alkylene, more
particularly C.sub.1-4alkylene. Non-limiting examples of
C.sub.1-6alkylene groups include methylene (--CH.sub.2--), ethylene
(--CH.sub.2--CH.sub.2--), methylmethylene (--CH(CH.sub.3)--),
1-methyl-ethylene (--CH(CH.sub.3)--CH.sub.2--), n-propylene
(--CH.sub.2--CH.sub.2--CH.sub.2--), 2-methylpropylene
(--CH.sub.2--CH(CH.sub.3)--CH.sub.2--), 3-methylpropylene
(--CH.sub.2--CH.sub.2--CH(CH.sub.3)--), n-butylene
(--CH.sub.2--CH.sub.2--CH.sub.2--CH.sub.2--), 2-methylbutylene
(--CH.sub.2--CH(CH.sub.3)--CH.sub.2--CH.sub.2--), 4-methylbutylene
(--CH.sub.2--CH.sub.2--CH.sub.2--CH(CH.sub.3)--), pentylene and its
chain isomers, and hexylene and its chain isomers.
In particular embodiments, R.sup.10 is an ether or oligoether of
formula --R.sup.11[OR.sup.12].sub.mR.sup.13--, wherein R.sup.11,
R.sup.12 and R.sup.13 are independently from each other
C.sub.1-4alkylene; and m is an integer from 1 to 4. In further
embodiments, R.sup.11, R.sup.12 and R.sup.13 are independently from
each other C.sub.1-3alkylene; and m is an integer from 1 to 3.
In particular embodiments, R.sup.10 is C.sub.3-8cycloalkylene. As
used herein, the term "cycloalkylene", by itself or as part of
another substituent, refers to a cycloalkyl moiety as defined
herein which is divalent.
In a particular embodiment, R.sup.10 is C.sub.3-8cycloalkenylene.
As used herein, the term "cycloalkenylene" by itself or as part of
another substituent, refers to a cycloalkenyl as defined herein,
which is divalent. Preferred cycloalkenylene rings contain 5 or 6
ring atoms, such as cyclopentenylene and cyclohexenylene.
In particular embodiments, R.sup.10 is C.sub.6-10arylene. As used
herein, the term "arylene", by itself or as part of another
substituent, refers to an aryl moiety as defined herein which is
divalent.
In particular embodiments, R.sup.10 is C.sub.2-12alkenylene,
preferably C.sub.2-6alkenylene. The term "alkenylene" by itself or
as part of another substituent, refers to an alkenyl moiety as
defined herein, which is divalent.
In particular embodiments, R.sup.10 is C.sub.2-12alkynylene,
preferably C.sub.2-6alkynylene. The term "alkynylene" by itself or
as part of another substituent, refers to an alkynyl moiety as
defined herein, which is divalent.
In particular embodiments, R.sup.10 is heterocyclylene, preferably
a 3- to 8-membered heterocyclylene. The term "heterocyclylene" as a
group or part of a group, refers to a heterocyclyl moiety as
defined herein, which is divalent.
In particular embodiments, R.sup.10 is heteroarylene. The term
"heteroarylene", as used herein, refers to a heteroaryl moiety as
defined herein, which is divalent.
In particular embodiments, R.sup.10 is C.sub.7-16aralkylene. The
term "aralkylene" as a group or part of a group, refers to an
aralkyl moiety as defined herein, which is divalent.
In particular embodiments, R.sup.10 is "C.sub.7-16alkylarylene".
The term "alkylarylene", as a group or part of a group, refers to
an alkylarylene as defined herein, which is divalent.
In particular embodiments, R.sup.10 is
heterocyclylC.sub.1-6alkylene. The term
"heterocyclylC.sub.1-6alkylene", as a group or part of a group,
refers to a heterocyclylC.sub.1-6alkyl moiety as defined herein,
which is divalent.
In particular embodiments, R.sup.10 is heteroarylC.sub.1-6alkylene.
The term "heteroarylC.sub.1-6alkylene", as a group or part of a
group, refers to a heteroarylC.sub.1-6alkyl as defined herein,
which is divalent.
In particular embodiments, R.sup.10 is
C.sub.4-10cycloalkylalkylene, more particularly
C.sub.4-8cycloalkylalkylene. The term "cycloalkylalkylene" as a
group or part of a group, refers to a cycloalkylalkylene as defined
herein, which is divalent.
In a particular embodiment, R.sup.10 is
C.sub.4-10cycloalkenylalkylene. As used herein, the term
"C.sub.4-10cycloalkenylalkylene" as a group or part of a group,
means an cycloalkenyl-alkylene in which the cycloalkenyl and
alkylene are as defined herein, wherein the cycloalkenyl and
alkylene together contain 4 to 10 carbon atoms.
The term "halo" or "halogen" as used herein refers to fluoro,
chloro, bromo or iodo.
The term "amino" by itself or as part of another substituent,
refers to --H.sub.2.
The term "hydroxyl" by itself or as part of another substituent,
refers to --OH.
The term "sulfhydryl", by itself or as part of another substituent,
refers to an --SH group.
The term "cyano", by itself or as part of another substituent,
refers to an --CN group.
The term "phosphonate" as used herein includes phosphonic acids,
and esters or salts thereof. The term "phosphinate" as used herein
includes phosphinic acids, and esters or salts thereof.
The metal or silicon oxides and hydroxides envisaged for use in the
membranes described herein may be porous. The term "porous" as used
herein refers to solid materials with pores, i.e. cavities,
channels or interstices. The skilled person will understand that
for the internal coating of small pores, the groups R.sup.1,
R.sup.1', and R.sup.10 as described herein preferably are as small
as possible. For example, R.sup.1 and R.sup.1' may be methyl or
phenyl, and R.sup.10 methylene. Such short groups typically provide
the best protection against fouling. However, larger groups may
still be suitable for coating the outer surface of an oxide or
hydroxide, or the inner surface of larger pores.
The present application relates to the field of membranes for
filtration, in particular ceramic microfiltration, ultrafiltration
or nanofiltration membranes.
The term "nanofiltration", "ultrafiltation" or "microfiltration" as
used herein refers to filtration using size exclusion by means of a
porous membrane, which will allow the passage of solvents while
retarding the passage of larger solute molecules, when a pressure
gradient is applied across the membrane. Typically, microfiltration
membranes have pore sizes in the range of 0.1 micrometer, capable
of retaining viruses and bacteria. Typically, ultrafiltration
membranes have pore sizes in the range of 2 to 50 nm. Typically,
nanofiltration membranes is characterized by molecular weight
cut-off values between 200 and 1000 Da, which makes 1-step removal
of bacteria, viruses, natural organic matter and micropollutants
feasible, without complete removal of inorganic salts. Therefore,
the pore size (equivalent diameter) of the nanofiltration membrane
is typically in the order of 1 nanometer. Typical values are
between 0.5 (tight NF) and 5 nm (open NF).
Provided herein are methods of protecting such membranes against
fouling. The advantages of the membranes envisaged herein apply to
microfiltration, ultrafiltration or nanofiltration membranes. In
particular embodiments the membranes envisaged are nanofiltration
membranes. Nanofiltration membranes have different applications.
One important application is to partially soften potable water,
allowing some minerals to pass into the product water and thus
increase the stability of the water and prevent it from being
aggressive to distribution piping material. Additionally,
nanofiltration membranes are finding increasing use for purifying
industrial effluents and minimizing waste discharge.
The methods described herein comprise the grafting of a membrane
comprising a silicon or metal oxide and/or hydroxide with an
organic moiety, by reacting said surface with an organometallic
reagent, a phosphonate, a phosphinate, or an organosilane
comprising said organic moiety (or a protected form or precursor
thereof). This will be explained more in detail herein below.
Functionalized Inorganic Matrix
The methods described herein allow for the protection of a membrane
comprising one or more oxides and/or hydroxides of metals or
silicon against fouling. Additionally or alternatively, these
methods may also be used for protecting metal or silicon oxides
and/or metal hydroxides which will be incorporated in filtration
membranes, against fouling.
In the present description, the one or more metal (or silicon)
oxides and/or metal (or silicon) hydroxides will be referred to as
"inorganic matrix". The term "inorganic matrix" may refer to the
metal (or silicon) oxides and/or metal (or silicon) hydroxides as
such, or in the form of a membrane. Accordingly, the term "matrix"
as used herein also refers to a "membrane". In further particular
embodiments the term "inorganic matrix" also refers to an
"inorganic membrane", also denoted herein as a "ceramic
membrane".
In certain embodiments of the methods and applications envisaged
herein, the functionalized matrix is an inorganic filtration
membrane or ceramic filtration membrane. As used herein, the
expression "inorganic filtration membrane" or "ceramic filtration
membrane" is intended to cover inorganic membranes which can be
used for microfiltration, ultrafiltration or nanofiltration. In
particular embodiments, the inorganic filtration membranes are
membranes which are suitable for the filtration of aqueous
compositions, more particularly compositions comprising at least 50
wt % (weight percent) water, preferably at least 70 wt % water,
more preferably at least 90 wt % water. Such compositions may
include, but are not limited to ground water, surface water, paper
pulp effluents, emulsions such as oil/water wastes (as will be
detailed below).
However, the membranes described herein may also show reduced
fouling when used for the filtration of non-aqueous compositions.
Accordingly, the functionalized membranes as described herein may
also be used for the treatment or filtration of non-aqueous
compositions.
Ceramic filtration membranes may have a variety of shapes. In
particular embodiments, the inorganic matrix described herein may
be in the form of a tube, sheet, disc or other shape that is
permeable to substances in solution.
Techniques for preparing such membranes are well known in the art.
A commonly used technique for preparing such filtration membranes
involves depositing one or more selective or filtering layers
(comprising the metal/silicon hydroxides and/or oxides) of a few
hundreds of nanometers or less in thickness onto a macroporous
support matrix which provides the mechanical strength. The
filtering layer is usually obtained by depositing mineral oxides
onto the matrix, followed by a final heat treatment.
The skilled person will understand that an inorganic matrix for use
in a liquid filtration membrane typically is porous. The pore size
may depend on the type of filtration which is desired, such as
microfiltration, ultrafiltration or nanofiltration (as explained
above). In certain embodiments the inorganic matrix is porous,
wherein the average pore size (or equivalent diameter) is between
0.5 to 200 nm, more preferably between 0.5 to 100 nm, more
preferably between 0.5 to 50 nm, more preferably between 0.5 to 30
nm, more preferably between 0.9 nm and 10.0 nm, as measured by
Molecular weight cut-off (indirect) and permporometry or nitrogen
sorption techniques applied on powders of the top layer (direct),
as known by the skilled person in the art.
In particular embodiments, the methods and applications envisaged
herein relate to an organically functionalized inorganic matrix,
wherein said matrix is a ceramic filtration membrane comprising a
support made of inorganic material coated with at least one
separating membrane layer having an average pore size of is between
0.5 to 200 nm, more preferably between 0.5 to 100 nm, more
preferably between 0.5 to 50 nm, more preferably between 0.5 to 30
nm, more preferably between 0.9 to 10 nm.
Inorganic membranes envisaged for use in the context of the present
methods comprise an inorganic matrix characterized by a structure
which can be represented by M.sup.1-OH and M.sup.1-O-M.sup.1
structure in which M.sup.1 is a metal or silicon. In the envisaged
methods, the surface modification typically involves the
replacement of hydroxyl (--OH) groups provided on the surface of
the membrane by organic functional groups.
The one or more metal oxides and/or hydroxides of the inorganic
matrix may be crystalline or non-crystalline (amorphous), or may
comprise a mixture of crystalline and amorphous phases. If the
inorganic matrix comprises silicon oxide and/or silicon hydroxide,
the silicon oxide and/or silicon hydroxide typically is amorphous.
Thus, the inorganic membranes envisaged herein typically comprise
an oxide and/or hydroxide of a metal; and/or an amorphous silicon
oxide.
The one or more elements M.sup.1 in the hydroxides or oxides
described herein are preferably selected from titanium, zirconium,
aluminium, silicon, strontium, yttrium, lanthanum, hafnium,
thorium, iron, and manganese and various possible mixtures thereof.
The above mentioned separating membrane layers are preferably
formed from transition metal oxide(s), more specifically selected
from group 4 of the IUPAC periodic table, in particular Ti and/or
Zr. In general, the inorganic matrix is preferably made of titanium
oxide and/or of zirconium oxide.
Examples of inorganic matrices that are envisaged for use in the
methods and applications described herein include for instance, but
are not limited to: a zirconium oxide matrix having a pore size of
3 nm or a titanium oxide matrix having a pore size of 0.9, 1 or 5
nm (purchasable from Inopor); a titanium oxide matrix with cut-off
of 5 or 10 kDalton (pore size on average 3 to 6 nm) (purchasable
from Atech); a mixed oxide matrix (titaniumoxide+zirconiumoxide)
with cut-off of 5 or 10 kDalton (pore size on average 3 to 6 nm)
(purchasable from Atech); and a titaniumoxide matrix with cut-off
of 1, 3, 5 or 8 kDalton (pore size on average 1 to 5 nm)
(purchasable from Tami Industries).
The methods described herein aim to reduce the sensitivity of an
inorganic matrix to fouling, by means of chemical surface
modification, also denoted as "functionalization". Thus, the
methods described herein generate a functionalized matrix, more
particularly an organically functionalized matrix. The terms
"organically functionalized matrix" or simply "functionalized
matrix" as used herein refers to an inorganic matrix of which the
surface properties have been changed or modified (functionalized)
by covalently binding an organic group R.sup.1 or R.sup.10
thereto.
In the context of the present application, the functionalization
results in a functionalized matrix which is more hydrophobic (i.e.
less hydrophilic) compared to the matrix before functionalization
(non-functionalized or native matrix). The increased hydrophobicity
can be assessed in various ways, e.g. via contact angle measurement
or flux measurements. More particularly, the functionalization as
described herein does not lead to an increased water flux, and will
typically result in a reduced water flux. In particular
embodiments, the water flux of the functionalized matrix is at
least 10% below the water flux of the non-functionalized matrix.
Preferably, the water flux is measured using deionized water in a
cross flow system, with a flow velocity of 2 m/s, a trans membrane
pressure (TMP) of 5 bar. In further embodiments, the water flux of
the functionalized matrix is at least 20% below or even at least
30% below the water flux of the non-functionalized matrix.
More particularly, the methods described herein involve
functionalizing an inorganic matrix comprising an oxide and/or
hydroxide of an element M.sup.1 which is a metal or silicon, by
functionalization of the surface of the inorganic matrix with an
organic moiety R.sup.1 or R.sup.10 in order to decrease the
sensitivity of the inorganic matrix to fouling. In certain
embodiments, the inorganic matrix may be functionalized with two
organic moieties (e.g. R.sup.1 and R.sup.1'), for example via
reaction of the inorganic matrix with a reagent of formula
R.sup.1-M.sup.2-R.sup.1' (see further), via reaction of the
inorganic matrix with a mixture of reagents, and/or via iteration
of the method on the same inorganic matrix using different
reagents. R.sup.1 and R.sup.1' may be the same or different.
It has been found that the functionalization of the membranes with
specific organic moiety R.sup.1 or R.sup.10 as described herein
decreases the sensitivity of the inorganic matrix to fouling. In
general, short R.sup.1 or R.sup.10 moieties are preferred.
Particularly preferred R.sup.1 or R.sup.10 moieties are provided
herein below.
In particular embodiments, R.sup.1 is selected from the list
consisting of C.sub.1-8alkyl, C.sub.6aryl, C.sub.7-10alkylaryl,
C.sub.7-10arylalkyl, --R.sup.7[OR.sup.8].sub.nR.sup.9,
C.sub.3-6cycloalkyl, C.sub.5-6cycloalkenyl,
C.sub.4-10cycloalkylalkyl, C.sub.6-10cycloalkenylalkyl,
C.sub.2-8alkenyl, 3- to 6-membered heterocyclyl, 5- to 8-membered
heteroaryl, heterocyclylC.sub.1-4alkyl, heteroarylC.sub.1-4alkyl
and C.sub.2-8alkynyl; wherein R.sup.7 and R.sup.8 are independently
from each other C.sub.1-3alkylene; n is an integer from 1 to 3; and
R.sup.9 is C.sub.1-3 alkyl; and
R.sup.10 is selected from the list consisting of C.sub.1-8alkylene,
C.sub.6arylene, C.sub.7-10alkylarylene, C.sub.7-10arylalkylene,
--R.sup.11[OR.sup.12].sub.mR.sup.13, C.sub.3-6cycloalkylene,
C.sub.5-6cycloalkenylene, C.sub.4-10cycloalkylalkylene,
C.sub.6-10cycloalkenylalkylene, C.sub.2-8alkenylene, 3- to
6-membered heterocyclylene, 5- to 8-membered heteroarylene,
heterocyclylC.sub.1-4alkylene, heteroarylC.sub.1-4alkylene and
C.sub.2-8alkynylene; wherein R.sup.11, R.sup.12 and R.sup.13 are
independently from each other C.sub.1-3alkylene; and m is an
integer from 1 to 3. In certain embodiments, R.sup.1 is selected
from the list consisting of C.sub.1-6alkyl, phenyl,
C.sub.7-8alkylaryl, C.sub.7-8arylalkyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.3-6cycloalkyl,
C.sub.5-6cycloalkyl, C.sub.4-7cycloalkylalkyl,
C.sub.6-8cycloalkenylalkyl, C.sub.2-6alkenyl, 3- to 6-membered
heterocyclyl, 5- to 6-membered heteroaryl,
heterocyclylC.sub.1-3alkyl, heteroarylC.sub.1-3alkyl and
C.sub.2-6alkynyl; wherein R.sup.7 and R.sup.8 are independently
from each other C.sub.1-2alkylene; n is an integer from 1 to 3; and
R.sup.9 is C.sub.1-2 alkyl; and R.sup.10 is selected from the list
consisting of C.sub.1-6alkylene, phenylene, C.sub.7-8alkylarylene,
C.sub.7-8arylalkylene, --R.sup.11[OR.sup.12].sub.mR.sup.13,
C.sub.3-6cycloalkylene, C.sub.5-6cycloalkenylene,
C.sub.4-7cycloalkylalkylene, C.sub.6-8cycloalkenylalkylene,
C.sub.2-6alkenylene, 3- to 6-membered heterocyclylene, 5- to
6-membered heteroarylene, heterocyclylC.sub.1-3alkylene,
heteroarylC.sub.1-3alkylene and C.sub.2-6alkynylene; wherein
R.sup.11, R.sup.12 and R.sup.13 are independently from each other
C.sub.1-2alkylene; and m is an integer from 1 to 3. In certain
embodiments, R.sup.1 is selected from the list consisting of
C.sub.1-6alkyl, phenyl, benzyl, tolyl,
--R.sup.7[OR.sup.8].sub.nR.sup.9, C.sub.2-6alkenyl, furyl,
1-furylmethyl, and 1,3-dioxolan-2-ylmethyl; and R.sup.10 is
C.sub.1-6alkylene; wherein R.sup.7 and R.sup.8 are independently
from each other C.sub.1-2alkylene; n is an integer from 1 to 3; and
R.sup.9 is C.sub.1-2 alkyl.
In certain embodiments, R.sup.1 is selected from the group
consisting of C.sub.1-6alkyl, phenyl, and benzyl. Such groups were
found to provide excellent antifouling properties. In specific
embodiments, R.sup.1 is selected from the group consisting of
C.sub.1-6alkyl and phenyl, more particularly methyl or phenyl. In
certain embodiments, R.sup.1 is C.sub.1-6alkyl, preferably selected
from methyl, ethyl, and propyl.
Optionally, the membranes may further be grafted with one or more
moieties R.sup.1' which can be the same or different from R.sup.1.
In certain embodiments, R.sup.1 and R.sup.1' are identical. If
R.sup.1 and R.sup.1' are not identical, R.sup.1' typically is less
bulky than R.sup.1. More particularly, R.sup.1' preferably
comprises less carbon atoms than R.sup.1.
In particular embodiments, said R.sup.1, R.sup.1', and/or R.sup.10
as described above may be further substituted with one or more
groups selected from hydroxyl, --OR.sup.4, amino, halo, sulfhydryl,
--SR.sup.5, --COOH, and --COOR.sup.6; wherein R.sup.4, R.sup.5, and
R.sup.6 are independently selected from C.sub.1-6alkyl, halo and
C.sub.6-10aryl. In certain embodiments, the one or more
substituents are independently selected from hydroxyl, amino, halo,
sulfhydryl, and --COOH.
The skilled person will understand that only a limited number of
hydrophilic substituents such as hydroxyl should be used in order
to ensure a functionalization which renders the inorganic matrix
more hydrophobic compared to the native inorganic matrix. More
particularly, the number and/or position of the optional
substituents can be selected so as to ensure a decreased
hydrophilicity (i.e. an increased hydrophobicity) of the grafted
membrane compared to the native membrane (i.e. the membrane before
grafting).
It is however envisaged that in other embodiments, said R.sup.1,
R.sup.1' and/or R.sup.10 as described above may not be provided
with further substituents.
The functionalization or grafting of the surface of the inorganic
matrix with an organic moiety R.sup.1 or R.sup.10 may be obtained
by reacting the inorganic matrix with one or more organometallic
reagents, phosphonates, phosphinates, and/or organosilanes. This
will be explained in more detail herein below.
Reaction with Organometallic Reagent
In particular embodiments, the method for protecting an oxide or
hydroxide against fouling as described herein may involve grafting
the surface of the inorganic matrix with an organic moiety R.sup.1
via reaction with an organometallic reagent, such as a Grignard
reagent and/or an organolithium reagent.
A procedure for the functionalization of an inorganic matrix via
reaction with organometallic chemistry suitable for use in the
present method, is based on the method for obtaining a
functionalized matrix as described in international patent
application WO 2010/106167, which is hereby incorporated by
reference. Thus, in certain embodiments, the reaction of the
inorganic matrix with the organometallic reagent comprises an
appropriate pretreatment of the inorganic matrix, including drying
the matrix; reacting the dried matrix in the presence of a dry
solvent with said organometallic reagent, thereby obtaining a
functionalized matrix; and optionally, washing and drying the
functionalized matrix.
The functionalization via reaction with an organometallic compound
as described in WO 2010/106167 results in the functionalization of
the matrix with one or more R.sup.1 (and optionally R.sup.1')
moieties, as defined herein, that are directly bound covalently to
an element M.sup.1 (being a metal or silicon) on a surface of said
matrix via a direct M.sup.1-R.sup.1 bond. More particularly, the
direct M.sup.1-R.sup.1 bond can be obtained via a direct M.sup.1-C
bond i.e. not including an oxygen bridge.
If M.sup.1 is a metal, this can improve the stability of the
obtained matrix, compared to grafting with an organosilane, which
typically forms a M.sup.1-O--Si--R covalent bond which is more
sensitive to hydrolysis.
Organometallic reagents as used herein may be represented by
formula R.sup.1-M.sup.2, or formula R.sup.1-M.sup.2-X, or formula
R.sup.1-M.sup.2-R.sup.1', wherein R.sup.1 and R.sup.1' can be
different or identical and are moieties as defined above, M.sup.2
is a metal selected from group 1 or 2 of the IUPAC periodic table,
more particularly selected from Li and/or Mg, and wherein X is
halo. It is noted that where R.sup.1 and/or R.sup.1' as defined
above comprises a functional group which is not compatible with
organometallic compounds, such group should be provided in a
protected form (i.e. with a protective group). Protective groups
are well known in the art and will not be disclosed in detail
herein.
In particular embodiments, the organometallic reagent is an
organolithium reagent or an organomagnesium reagent. An
organolithium reagent is an organometallic compound with a direct
bond between a carbon and a lithium atom and may be represented by
the general formula R.sup.1--Li wherein R.sup.1 is a moiety as
defined herein above. Preferred organolithium compounds are
C.sub.1-4alkyllithium such as methyllithium, and phenyllithium.
Reaction of an inorganic matrix with such organolithium reagents
can result in a functionalized matrix which is particularly
resistant to fouling.
An organomagnesium reagent is an organometallic compound with a
direct bond between a carbon and a magnesium atom and may be
represented by the general formula R.sup.1--Mg--X (Grignard
reagent) or R.sup.1--Mg--R.sup.1', wherein R.sup.1 and R.sup.1' are
moieties as defined herein and wherein R.sup.1 and R.sup.1' can be
different or identical, and wherein X is halo, and preferably
bromo, chloro, or iodo. A preferred organometallic reagent for use
in the present method is a Grignard reagent. Particularly preferred
Grignard reagents are C.sub.1-4alkyllmagnesium halide such as
methylmagnesium halide, and phenylmagnesium halide. Reaction of an
inorganic matrix with such Grignard reagents can result in a
functionalized matrix which is particularly resistant to
fouling.
In particular embodiments, of the matrix may be reacted with two or
more different organometallic reagents, thereby allowing to
directly bind on a surface of an inorganic membrane two or more
different types of moieties.
Reaction with Phosphonate or Phosphinate
In particular embodiments, the method for protecting an oxide or
hydroxide against fouling as described herein may involve grafting
the surface of the inorganic matrix with an organic moiety R.sup.1
or R.sup.10 via reaction with a phosphonate and/or a phosphinate.
In contrast with the reaction with organometallic reagents as
described above, some phosphonate reactions may be performed using
aqueous solutions or organic solutions which do not need to be
dried. Nevertheless, phosphonate or phosphinate reactions may also
be performed in dried organic solvents.
Various procedures for the functionalization of an inorganic matrix
via a (condensation) reaction with phosphonates which are suitable
for use in the present method are known in the art. An example of a
suitable procedure is the one described in patent application US
2002/0023573, which is hereby incorporated by reference.
The functionalization via reaction with an phosphonate or
phosphinate as described therein results in the functionalization
of the matrix with a R.sup.1 moiety, as defined herein, that are
bound covalently to a metal (or silicon) M.sup.1 on a surface of
said matrix via a covalent M.sup.1-O--P--R.sup.1 bond, more
particularly via a covalent M.sup.1-O--P--C bond. With
phosphonates, the same phosphorous atom may be bound to the matrix
via a mono-, bi-, or tridentate bond (i.e. via one, two, or three
P--O-M.sup.1 bonds). The M.sup.1-O--P--R.sup.1 bond typically
provides sufficient stability for use of the functionalized
material in filtration, for cleaning of the material, etc.
In particular embodiments, the inorganic matrix may be reacted with
a diphosphonate or diphosphinate. This can result in the
functionalization of the matrix with a R.sup.10 moiety, as defined
herein, that is bound to a metal (or silicon) M.sup.1 on a surface
of said matrix via two covalent bonds, forming a bridged structure,
represented by M.sup.1-O--P--R.sup.10--P--O-M.sup.1. Accordingly,
R.sup.10 can be bound to two elements M.sup.1 (which can be the
same or different) of the inorganic matrix, thus forming a bridge.
This can increase the stability of the functionalized matrix.
Again, with phosphonates, the same phosphorous atom may be bound to
the matrix via a mono-, bi-, or tridentate bond.
It is noted that where R.sup.1 or R.sup.10 as defined above
comprises a functional group which is not compatible with the
functionalization process (via reaction with organometallic
reagents or phosphonates), such group should be provided in a
protected form (i.e. with a protecting group), that is to be
removed after functionalization. Protecting groups, and the methods
for removing them are well known in the art and will not be
disclosed in detail herein.
In particular embodiments, the grafting described herein may
involve grafting the surface of the inorganic matrix with an
organic moiety R.sup.1 via reaction with a phosphonate reagent.
More particularly, said phosphonate reagent is a compound having a
formula corresponding to the structures herein below. In particular
embodiments, said phosphonate is a compound of formula (I)
##STR00004## or a salt or ester thereof, wherein R.sup.1 has the
same meaning as described above.
Preferred salts or esters of the compound of formula (I) are
phosphonates of formula (II)
##STR00005## wherein R.sup.1 has the same meaning as described
above; and wherein R.sup.2 and R.sup.3 are independently selected
from hydrogen, C.sub.1-18alkyl, C.sub.6-14aryl, and
C.sub.3-16cycloalkyl. In certain embodiments, R.sup.2 and R.sup.3
are independently selected from hydrogen, halo, and
C.sub.1-12alkyl. In esters or salts of the compound of formula
(II), at least one of R.sup.2 and R.sup.3 is not hydrogen.
Preferred phosphinates are phosphinates of formula (III)
##STR00006## or a salt or ester thereof, wherein R.sup.1 and
R.sup.1' are as defined above.
Preferred diphosphonates are compounds of formula (IV)
##STR00007## or a salt or ester thereof, wherein R.sup.10 has the
same meaning as described above.
In particular embodiments, the grafting described herein may
involve grafting the surface of the inorganic matrix with an
organic moiety R.sup.1 or R.sup.10 via reaction with a phosphonate
reagent, wherein said phosphonate is a compound selected from the
group consisting of methylphosphonic acid, phenylphosphonic acid,
2-(2-ethoxyethoxy)ethylphosphonic acid, 6-phosphonohexanoic acid,
1-[2-(2-diethoxyphosphorylethoxy)ethoxy]-2-methoxy-ethane,
5-diethoxyphosphorylhexan-1-ol, 10-diethoxyphosphoryldecanoic acid,
methyl 10-diethoxyphosphoryldecanoate, and
3-phosphonopropylphosphonic acid. In certain embodiments, the
phosphonate reagent is methylphosphonic acid and/or
phenylphosphonic acid.
In particular embodiments, the present method for protecting an
oxide or hydroxide against fouling as may involve contacting the
inorganic matrix with a solution comprising the phosphonic acid,
and letting the phosphonic acid react with the surface of the
inorganic matrix.
The reaction may be carried out at room temperature, or at elevated
temperatures, e.g. under reflux conditions. In preferred
embodiments, the reaction is carried out at a temperature between
20.degree. C. and 150.degree. C., and preferably between 20.degree.
C. and 100.degree. C.
In order to obtain a sufficient functionalization of the inorganic
matrix, the reaction is preferably carried out during a period of
at least 30 minutes, preferably between one hour and 24 hours,
under conditions of stirring and/or shaking of the reaction
mixture, or while filtrating the reaction mixture through the
membrane.
Optionally, the inorganic matrix may be washed after reaction,
using an appropriate solvent, i.e. appropriate to dissolve the
reaction products. Typically, this can be done using water, or the
solvent applied in the synthesis. The washing process can be
repeated if necessary. Preferably washing is done by means of
filtration through the membrane pores, in particular to prevent
that reaction products would remain on the matrix and in the pores
of the matrix. Preferably filtration is done under pressure.
The grafting procedure may further optionally comprise the step of
drying the obtained matrix, preferably under vacuum. The drying of
the matrix may be done in a similar way as described above for the
reaction with organometallic reagents.
Reaction with Organosilane Reagent
In particular embodiments, the method for protecting an oxide or
hydroxide against fouling as described herein may involve grafting
the surface of the inorganic matrix with an organic moiety R.sup.1
or R.sup.10 via reaction with an organosilane reagent.
Reaction of the inorganic matrix with an organosilane results in
the functionalization of the matrix with a R.sup.1 moiety which is
bound covalently to a metal (or silicon) M.sup.1 on a surface of
said matrix via a covalent M.sup.1-O--Si--R.sup.1 bond, more
particularly via a covalent M.sup.1-O--Si--C bond.
As described above, the M.sup.1-O--Si--R.sup.1 bond typically is
less stable than a direct M.sup.1-R.sup.1 bond if M.sup.1 is metal.
However, if M.sup.1 is silicon, the M.sup.1-O--Si--R.sup.1 bond
provides an excellent stability. In certain embodiments, R.sup.1 is
bound covalently to M.sup.1 via a covalent M.sup.1-O--Si--R.sup.1
bond, provided that M.sup.1 is silicon.
In particular embodiments, the inorganic matrix may be reacted with
a disilane. This can result in the functionalization of the matrix
with a R.sup.10 moiety, as defined above, that is bound to M.sup.1
via two covalent bonds, forming a bridged structure, represented by
M.sup.1-O--Si--R.sup.10--Si--O-M.sup.1. Accordingly, R.sup.10 can
be bound to two elements M.sup.1 (which can be the same or
different) of the inorganic matrix, thus forming a bridge. This can
increase the stability of the functionalized matrix.
Various procedures for the functionalization of an inorganic matrix
via a (condensation) reaction with organosilanes which are suitable
for use in the present method are known in the art. An example of a
suitable procedure is the one described in patent application US
2006/237361, which is hereby incorporated by reference.
In particular embodiments, the organosilane grafting described
herein may involve grafting the surface of the inorganic matrix
with an organic moiety R.sup.1 via reaction with an organosilane
reagent of formula R.sup.1XYZSi, wherein R.sup.1, X, Y, and Z are
directly bound to Si; and R.sup.1 has the same meaning as defined
above. At least one of X, Y, and Z is a hydrolysable group, wherein
the others are independently have the same meaning as R.sup.1' as
defined above. In particular embodiments, the organosilane is a
compound of formula (R.sup.1).sub.3XSi, wherein X is a hydrolysable
group. Suitable hydrolysable groups include, but are not limited to
halo, and C.sub.1-8alkoxy such as methoxy (CH.sub.3O--) or ethoxy
(CH.sub.3CH.sub.2O--).
In particular embodiments, the organosilane grafting described
herein may involve grafting the surface of the inorganic matrix
with an organic moiety R.sup.10 via reaction with a disilane
reagent of formula (XYZ)SiR.sup.10Si(XYZ), wherein R.sup.10 has the
same meaning as defined above. Again, at least one of X, Y and Z is
a hydrolysable group, wherein the others independently have the
same meaning as R.sup.1' as defined above. In particular
embodiments, the disilane is a compound of formula
(X').sub.3Si--R.sup.10--Si(X').sub.3.
In particular embodiments, the organosilane grafting may involve an
appropriate pre-treatment of the inorganic surface, contacting the
inorganic matrix with a solution comprising the organosilane
reagent, and letting the organosilane reagent react with the
surface of the inorganic matrix, as known in the art.
Repetition of the Functionalization
In particular embodiments of the method described herein, the
functionalization via reaction with an organometallic reagent or a
phosphonic acid reagent may be repeated one or more times on the
same inorganic matrix. Repeated modifications can for instance be
applied to increase the amount of organic functional group(s) on
the surface of the membrane. However, as the functionalization
described herein typically results in a reduced flow it is
preferred to provide the grafting as a submonolayer, which means
that the surface of the inorganic matrix is not fully saturated
with functional groups. In this way, the membranes can be protected
against fouling while minimizing flux reduction.
Repeated functionalization may also permit to bind two or more
different types of organic groups directly on a surface of a
filtration membrane. Alternatively or in combination therewith,
different types of organic groups can also be covalently bound by
simultaneously reacting the inorganic matrix with two or more
different organometallic reagents, or two or more different
phosphonic acids as described above.
In particular embodiments, a functionalization using an
organometallic reagent may be followed by a further
functionalization using a phosphonic acid reagent, or vice
versa.
Membrane
The methods envisaged herein result in functionalized inorganic
matrices which can be used as filtration membranes and provide an
increased resistance to fouling compared to non-functionalized
inorganic matrices. Moreover, the functionalization via a direct
M.sup.1-C bond, an M.sup.1-O--P--C bond, or an M.sup.1-O--Si--C
bond (particularly when M.sup.1 is Si) provides a satisfactory
chemical, mechanical, thermal and hydrothermal stability.
Accordingly, further provided herein are functionalized inorganic
matrices, obtainable by or obtained by the methods described
herein. More particularly, such membrane may comprise an oxide
and/or hydroxide of an element M.sup.1 which is a metal or silicon,
wherein the surface of said inorganic matrix is grafted, preferably
covalently grafted, with an organic functional group R.sup.1, via a
direct M.sup.1-R.sup.1 bond; at least one M.sup.1-O--P--R.sup.1
bond; a M.sup.1-O--Si--R.sup.1 bond; a
M.sup.1-O--P--R.sup.10--P--O-M.sup.1 bond; or a
M.sup.1-O--Si--R.sup.10--Si--O-M.sup.1 bond; wherein R.sup.1 and
R.sup.10 are as defined above.
In particular embodiments, M.sup.1 is selected from the group
consisting of titanium, zirconium, aluminium, silicon, strontium,
yttrium, lanthanum, hafnium, thorium, iron, manganese, or
combinations thereof. In certain embodiments, M.sup.1 is Ti and/or
Zr. In specific embodiments, the oxide and/or hydroxide of M.sup.1
is titanium oxide or zirconium oxide.
In particular embodiments, the filtration membrane may comprise a
support made of inorganic material coated with at least one
separating membrane layer made of the oxide and/or hydroxide of
metal M.sup.1 at the surface. In certain embodiments, the oxide
and/or hydroxide of M.sup.1 may be provided as particles in a mixed
matrix membrane. For example, the particles may be embedded in a
polymer matrix. The preparation of mixed matrix membranes is
well-known in the art. For example, the particles may be assembled
on the surface of a (porous) membrane, or the particles may be
blended with a (polymeric) casting solution. An overview of
manufacturing procedures is provided by Kim and Van der Bruggen
(Environmental Pollution 2010, 158, 2335-2349). The particle size
and amount of particles and (polymer) matrix material can be chosen
depending on the required characteristics of the membranes. In
certain embodiments, the membranes are porous, having an average
pore size of 0.5 nm to 200 nm, more particularly 0.5 nm to 30 nm,
for example 0.9 nm to 10 nm.
As is known by a person skilled in the art, it is not easy to
directly analyze the changes on the surface of a modified membrane
toplayer, whether the modification is done by the procedures as
described herein or via other modification techniques known in the
state of the art such as silanation. This is due to the fact that
the modification takes place in the pores of the thin toplayer,
while the bulk of the membrane (support and intermediate layers)
are not or hardly modified, such that the presence of the much
thicker membrane support masks the properties of the membrane
toplayer; and/or because of the curvature of the membrane, which
may e.g. have a tubular shape. Therefore, an unsupported membrane
toplayer material may be used in order to characterize the
properties of the supported membrane toplayer, which is made in
exactly the same way as the supported membrane toplayer. Suitable
characterization methods for such samples include Thermal
Gravimetric Analysis (TGA), IR spectroscopy solid state NMR, XPS
and leaching tests or other methods known in the art, as described
in international patent application WO 2010/106167, which is hereby
incorporated by reference.
Flux measurements do not directly analyse the modification of the
membrane surface, but are a suitable way to determine the effect of
the membrane modification on the membrane performance. In case of
hydrophobic modification with e.g. alkyl chains, the flux of apolar
solvents will increase, while the flux of polar solvents such as
water will be similar or decrease. Another indirect
characterization technique determining the effect of the membrane
modification on the membrane performance is a molecular weight
cut-off (MWCO) measurement, permporometry and/or a (water) contact
angle measurement. This is illustrated in the Examples (see
further).
Use in Water Filtration
It has surprisingly been found that the organically functionalized
matrices as envisaged herein are particularly suitable for use in
water treatment, more particularly water purification. Indeed, it
has been found that despite the functionalization with organic
moieties, which in fact increases their hydrophobicity, the
membranes remain suitable for filtration of aqueous compositions.
As used herein, the term "water purification" refers to
purification of (or removal of contaminants from) aqueous
compositions comprising more than 50 wt % water, more particularly
at least 70 wt % water.
More particularly it has been found that the membranes are
resistant to fouling agents of aqueous compositions such as ground
water or surface water. Most particularly the organically
functionalized matrices are of interest in the treatment of ground
water or surface water, as they have a reduced sensitivity for
fouling by foulants such as humic acids in combination with
inorganic salts (e.g. Ca.sup.+2), proteins, peptides, amino acids,
polysaccharides and transparent exopolymer particles (TEP). But the
organically functionalized matrices are also of interest in the
treatment of different waste-waters as for example (but not limited
to) paper and pulp effluents, and emulsions such as oil/water waste
waters.
Inorganic matrices envisaged for use in water filtration are
typically made of one or more metal oxides and/or metal hydroxides
due to their inherent hydrophilic nature. Typically, their surface
chemistry essentially consists of a M.sup.1-OH and
M.sup.1-O-M.sup.1 structure in which M.sup.1 is a metal or silicon.
The methods and applications described herein envisage the use of
such inorganic matrices which have been organically
functionalized.
Accordingly, envisaged herein is the use of organically
functionalized inorganic matrices comprising an oxide and/or
hydroxide of a metal M.sup.1 for water treatment, whereby the
matrices are characterized in that their surface is grafted,
preferably covalently grafted, with an organic functional group.
More particularly, the organic group is a group such as but not
limited to a group R.sup.1 or R.sup.10 as defined above.
It is envisaged that the functionalization of the element M.sup.1
in the matrix is not critical and can be ensured either through a
direct bond with the metal or through an oxygen bridge. In
particular embodiments, the bond is a direct M.sup.1-C bond, an
M.sup.1-O--P--C bond, or an M.sup.1-O--Si--C bond. In particular
embodiments M.sup.1 is selected from the group consisting of
titanium, zirconium, aluminum, silicon, strontium, yttrium,
lanthanum, hafnium, thorium, iron, manganese, or combinations
thereof. More particularly, the metal is titanium and/or
zirconium.
The organically functionalized matrices for use as water treatment
membranes can be obtained as described herein above.
Thus provided herein are methods of treating aqueous solutions,
such as methods for the removing impurities from aqueous solutions,
comprising filtering said aqueous solutions with the matrices or
membranes described herein above obtainable by or obtained by the
methods described herein above. In particular embodiments, the
membranes are used for the (nano)filtration of aqueous compositions
comprising at least 50 wt % water, preferably at least 75 wt %
water, and more preferably at least 90 wt % water. In further
particular embodiments, the water is groundwater, or surface water
of industrial waste waters.
Practical examples where the anti-fouling effect is of critical
importance include, but are not limited to, the production of
drinking water from ground water or other sources of water, the
purification of different waste waters including pulp and paper
effluents, oil/water effluents (from olive oil production, or
oil/water emulsions found in water that is used to pump up oil
etc.) Further provided herein is a method of purifying an aqueous
composition, said method comprising providing a filtration membrane
comprising a functionalized inorganic matrix comprising an oxide
and/or hydroxide of an element M.sup.1 wherein M.sup.1 is a metal
or silicon, characterized in that the surface of the inorganic
matrix is grafted with an organic functional group R.sup.1 or
R.sup.10 as described herein; and filtering said aqueous
composition through said membrane so as to obtain a purified
aqueous composition.
Thus methods are provided herein for purifying an aqueous
composition, the method comprising filtering said aqueous
composition through a filtration membrane comprising a
functionalized inorganic matrix comprising an oxide and/or
hydroxide of an element M.sup.1 wherein M.sup.1 is a metal or
silicon, characterized in that the surface of the inorganic matrix
is grafted with an organic functional group R.sup.1 or R.sup.10 as
described herein and obtaining in the filtrate a purified aqueous
composition. In particular embodiments, the purification
encompasses the removal of contaminants such as oil, humics and/or
other natural organic matter, and/or polyelectrolytes. In
particular embodiments, the methods ensure the removal of oils or
petroleum products. In particular embodiments, at least 90% of the
contaminants is removed from the aqueous composition via filtering
through the membrane, preferably at least 95%.
EXAMPLES
The following examples are provided for the purpose of illustrating
the claimed methods and applications and by no means are meant and
in no way should be interpreted to limit the scope of the present
invention.
1. Fouling Prevention in Surface and Ground Water Treatment
Commercially available titanium oxide (TiO.sub.2) NF membranes were
grafted with various organic moieties applying both Phosphonic
acids and Grignard grafting techniques. Hydrophilicity, pore size,
and other structural changes after graftings were investigated by
measuring water contact angles, molecular weight cut-off values,
and water permeabilities. Subsequently, the grafted membranes with
the highest water flux were subjected to fouling measurements with
model foulants mimicking the fouling in surface and ground water
treatment for drinking water production, and with model fouling
solutions mimicking the fouling in the effluents of pulp and paper
industry. Similar tests were performed on a native (i.e. unmodified
or non-functionalized) membrane as a control. This is explained
further herein below.
1.A) Materials and Methods
Membranes and Chemicals
Asymmetric TiO.sub.2 NF tubular membranes having an outer diameter
of 1 cm, an inner diameter of 0.7 cm, and 12 cm in length (active
membrane surface area .about.20 cm.sup.2) with an average pore
diameter of 0.9 nm were obtained from Inopor Gmbh, Germany.
All reagents and other chemicals were obtained from Sigma Aldrich:
grafting reagents (methyl, phenyl, and hexadecyl phosphonic acids;
methyl and phenyl magnesium bromide), model foulants (humic acid,
meat peptone, laminarin), toluene, CaCl.sub.2, NaOH, and HCl (of pH
adjustment). The alkaline cleaning agent P3 Ultrasil 110 was
obtained from Ecolab. Reverse osmosis (RO) water with a
conductivity of less than 15 .mu.s/cm and pH 6.5 was used for all
filtration experiments and for phosphonic acids grafting.
Grignard Grafting
TiO.sub.2 membranes were grafted with methyl or phenyl groups using
the organometallic Grignard reagents methyl magnesium bromide and
phenyl magnesium bromide, respectively. In a first step, the
membranes were properly pretreated to remove the adsorbed water of
the membrane surface. Subsequently, the pretreated membranes were
contacted (with stirring and shaking or with filtration) for 48
hours to a reaction mixture of Grignard reagent in diethyl ether,
under sufficiently dry atmosphere. The total metal oxide pore
surface reacts with the Grignard reagent and the intended groups
are grafted on the membrane. MgBr salts are formed as side products
of the reaction. These have been washed by a proper washing
procedure. After washing, the membranes have been dried at
60.degree. C. under vacuum before use in performance tests.
Phosphonic Acid Grafting
TiO.sub.2 membranes were grafted with methyl, phenyl, and hexadecyl
groups using methylphosphonic acid, phenylphosphonic acid, and
hexadecylphosphonic acid, respectively.
In a first step, the membranes were immersed in a solution of
methyl-, phenyl-, or hexadecylphosphonic acid (0.01 to 0.1 M) in
water or toluene, and treated for 4 hours at room temperature or
for 4 hours under reflux at 90.degree. C., under stirring and
shaking. The modified membranes were separated by pouring out the
reaction solution after 4 hours. Subsequently, the membranes were
properly washed at room temperature with the reaction solvent
(85-90 ml for 30 min with 5 times repetition), again under stirring
and shaking. Thereafter, the membranes were fixed in a dead-end
set-up at a pressure of 2 bar for washing with water inside of the
pores. Subsequently, the membranes were dried at room temperature
before use in performance tests.
Water Contact Angle, Permeability, and MWCO Measurement
Grafted and ungrafted membranes were characterized by measuring the
Molecular Weight Cut-Off (MWCO), the water contact angle, and the
water permeability of the membranes.
For the MWCO measurement, the membranes were analyzed via Gel
permeation chromatography using a Shimadzu system equipped with a
pump (LC-20AT), Auto sampler (sil 20AC HT), column oven (CTO-20AC)
and a refractive index detector (RID 10A)). The MWCO (i.e. the
molecular weight of the solute of which 90% is retained by the
membrane) was determined using the method as described by I. Genne
& G. Jonsson, C. Guizard, Harmonization of flux and MWCO
characterization methodologies, poster presentation in
international Congress on membrane and Membrane Processes (ICOM),
7-12 Jul. 2002, Toulouse, France. The water contact angle (CA) was
calculated using a contact angle system OCA 15 plus manufactured by
Dataphysics with the software package SCA 20.
Pure water flux was measured in a cross flow system, with a flow
velocity of 2 m/s, a trans membrane pressure (TMP) of 5 bar.
Fouling Measurements
The following procedure was adopted to evaluate the fouling
tendency of all membranes: 1. A reverse osmosis (RO) water flux
measurement is performed at room temperature in cross-flow (2 m/s,
5 bar TMP), for 1 to 3 hours in order to obtain a stable flux. 2.
Subsequently, fouling is induced by continuous filtration in
dead-end mode (to enhance the fouling effect) at room temperature
using a fouling solution, for 8 to 12 hours. 3. After fouling, a RO
water flux measurement was performed at room temperature in
cross-flow (again at 2 m/s and 5 bar TMP) to remove the reversible
part of the fouling. The measurements were performed for 1 to 3
hours in order to obtain a stable flux.
The loss in water flux determined in this way, is a measure for the
irreversible fouling. FIG. 2 graphically shows the RO water flux
through a membrane before fouling, the foulant solution flux and
the RO water flux after fouling. The difference between the RO
water flux after fouling and the foulant solution flux is referred
to as the amount of reversible fouling while the difference between
the RO water flux before and after fouling is referred to as the
amount of irreversible fouling. Flux values were calculated based
on the weight of the permeate, which was recorded automatically as
function of time.
Chemical Cleaning
The organically fouled membranes were cleaned using the alkaline
cleaning agent P3 ultrasil 110. The following solutions and
filtration conditions were used: 0.2 a 1% wt-solution of P.sub.3
ultrasil 110 (i.e. pH 9 to 12, conductivity 400 to 4220 .mu.s/cm),
temperature 46 to 60.degree. C., cross flow with a flow velocity of
about 4 m/s, TMP of 0.5 to 1 bar and a filtration time of 15 to 60
minutes. After cleaning, rinsing with RO water was performed (using
cross-flow filtration), and subsequently the water permeability was
determined.
1.B) Results
Membrane Functionalization
TiO.sub.2 membranes were grafted with either methyl (M), phenyl
(P), or hexadecyl (HD), via reaction with a phosphonic acid (PA) or
a Grignard reagent (GR). The smaller methyl and phenyl groups were
used to modify the outer membrane surface as well as the inner pore
surface of the membranes, whereas the hexadecyl functional groups
were grafted to only modify the outer surface of the membranes. The
resulting membranes are denoted by a three or four letter code,
wherein the last two letters indicate the grafting method (PA or
GR), and the first one or two letters indicate the grafted group
(M, P, or HD).
Membrane Characterization
In order to evaluate the impact of grafting of a specific
functional group applying a specific grafting method on the pore
structure and the hydrophilicity of the membranes, the molecular
weight cut-off (MWCO), water contact angle, and pure reverse
osmosis (RO) water permeability of the native and all grafted
membranes was measured. The experimental results are summarized in
Table 1.
TABLE-US-00001 TABLE 1 MWCO, CA, and RO water permeability values
of different modified membranes in comparison to an unmodified
native TiO.sub.2 0.9 nm NF membrane. MGR refers to methyl Grignard
membranes, PGR to phenyl Grignard membranes, MPA to
methylphosphonic acid grafted membranes, PPA to phenylphosphonic
acid grafted membranes and HDPA for hexadecylphosphonic acid
grafted membranes. Membranes ID CA (.degree.) Water permeability
(l/hm.sup.2bar) MWCO (Da) Native 20 20 512 MPA 37 14 500 PGR 60 8
542 MGR 60 9 511 PPA 80 low -- HDPA 124 zero --
The CA values show that the produced grafted membranes cover a wide
range of hydrophilicity depending on the grafting technique and the
grafted functional group. The water contact angle values correlate
with the water permeabilities, indicating that an increased
hydrophobicity of the membrane generally leads to a lower water
permeability. The PPA and HDPA membranes are most hydrophobic
(highest CA), leading to a significantly reduced water permeability
for the PPA membrane, and a water permeability of zero for the
HDPA. For these membranes, the MWCO value was not measured, and no
fouling experiments were performed.
For the other membranes, the MWCO values did not change
significantly after the different modifications in comparison to
unmodified membranes, indicating that no significant changes in
pore size occurred.
Fouling Measurements
Fouling experiments were performed using model fouling solutions
mimicking the fouling in surface and ground water treatment, and
model fouling solutions mimicking the fouling in the treatment of
effluents of pulp and paper industry.
Ground and surface water typically contain a number of common
foulants, more particularly humic acids with inorganic salts (e.g.
Ca.sup.+2), proteins, peptides, amino acids, polysaccharides and
transparent exopolymer particles (TEP). A number of synthetic
compounds mimicking these foulants are commercially available.
The fouling tendency of the grafted membranes in comparison to the
native membrane was determined by fouling measurements with the
following model foulants: humic acid in combination with different
concentrations of Ca.sup.2+ at different pH values, for mimicking
natural organic material (NOM) or humic materials; laminarin gum
for mimicking TEP foulants; and meat peptone, as a model foulant
for proteins.
A number of different aqueous solutions (foulant solutions) of
these model foulants and concentrations were prepared for measuring
the fouling tendency of modified membranes in comparison with
unmodified membranes. Concentrations and pH values used mimic those
of real ground and surface waters.
The same membranes were used for all three model foulants. In
between the measurements with the different type of foulants, the
fouled membranes were chemically cleaned (see further). The fouling
of the membranes was assessed by determining the decline of the RO
water flux values for each membrane, normalized to the RO water
flux before fouling. The results of the fouling experiments are
discussed herein below.
Fouling Using Humic Acid:
for the fouling experiments using humic acid, commercially
available humic acid (HA) was used as the model foulant, in a
concentration of 10 mg/L, in combination with 3 Ca.sup.2+
concentrations (1, 2 and 4 mmol) and 2 pH levels (6, 5 and 9). It
is known that inorganic ions, and in particular Ca.sup.2+ can
contribute to the adsorption of the organic matter to the membrane
surface, and that a higher ionic strength of the solution has a
positive effect on the adhesion of humic acids. The different
conditions were applied subsequently, without intermediate cleaning
of the membranes.
The results of the experiments are shown in FIG. 1A, and show a
clear water flux decline and thus irreversible fouling of the
native membrane under all conditions. On the other hand, less
fouling was observed with the MPA and PGR membranes, whereas no
fouling at all was observed with the MGR membrane. The visual
appearance of the membranes gave a similar indication of the degree
of fouling Indeed, whereas the MGR membrane still had its original
white color, the inside of the native membrane had a strong black
color after the fouling measurements. Also the MPA and PGR
membranes were colored due to fouling, but to a lesser extent than
the native membrane.
Fouling Using Laminarin:
It is well known that surface water is more fouling in the season
of algae bloom. In these periods, large and sticky transparent
exopolymer particles (TEP) are formed predominantly by
self-assembly of dissolved precursors, mostly dissolved
polysaccharides released by microorganisms as algea, phytoplankton
or bacterioplankton. Laminarin, a gum with a molecular size of
.about.30 kD, is an important part of TEPs, and is therefore used
as a model foulant in this study. Laminarin concentrations in real
water streams typically are in the range of (0-0.5) mg/l.
The results of the fouling experiments using laminarin are shown in
FIG. 1B. Again, the native membrane is clearly fouled. The results
of the PGR and the MGR membranes are similar to each other, and
each show a significantly lower fouling compared to the native
membrane. Also the fouling of the MPA membrane is low compared to
the native membrane.
Fouling Using Meat Peptone:
Next to humic acids, proteins, polysaccharides, fatty acids and
amino acids are the other main constituent of natural organic
matter (NOM) in ground and surface waters causing membrane fouling.
Commercial meat peptone, prepared by the enzymatic hydrolysis of
selected animal tissues, contains these compounds and is therefore
a suitable model foulant for these components. Again,
concentrations were used which mimics real streams: 5, 15 and 25
mg/L.
The results of the fouling experiments with meat peptone are shown
in FIG. 1C, and confirm the positive effect of the grafting on the
fouling behavior. Indeed, the MGR and MPA membrane again show a
remarkably low fouling, whereas also the fouling of the PGR
membrane is low compared to the native membrane.
Fouling Using Wood Extracts
Pulp and paper mill process waters or effluents typically comprise
a complex mixture of wood compounds (lignin, hemicelluloses, and
the like) and process chemicals (e.g. resin acids), which may have
a polymeric, oligomeric, or monomeric nature.
A model solution to mimic the fouling tendency of pulp and paper
mill process waters was prepared, based on a wood extract solution
extracted from wood at a high temperature provided by the
Lappeenranta University of Technology in Finland. The wood extract
solution was evaporated and the resulting powder was used to make
model solutions by diluting the powder into water at a
concentration of 1.1 and 2.2 g/L. The pH of the model solutions was
about 6.5. Such solutions comprise wood hemicelluloses and lignin
at wide molar mass range and a minor amount of wood lipophilic
extractives, and have shown a high fouling tendency for many
polymeric membranes.
Three grafted membranes (MGR, PGR and MPA) were used in fouling
measurements using these model solutions. The results of the
fouling experiments are shown in table 2 and FIG. 1D and again show
a positive effect of the grafting on the fouling behavior. More
particularly, the MGR and PGR membrane show a remarkably low
fouling, while the fouling of the MPA membrane is still
significantly lower compared to the native membrane.
TABLE-US-00002 TABLE 2 before fouling Pulp&Paper 1.1 g/l
Pulp&Paper 2.2 g/l MGR 1 1 0.9 PGR 1 0.96 0.86 Native 1 0.36
0.18 MPA 1 0.71 0.55
Membrane Cleaning
In between the measurements with the different foulants, all fouled
membranes were chemically cleaned with an alkaline cleaning agent.
After cleaning, the RO water flux of the membranes was measured in
order to evaluate the efficiency of the cleaning.
It was found that whereas all grafted membranes recovered
completely under milder chemical cleaning conditions at a pH value
of 10, the native membrane could not cleaned at pH10. Instead, the
native membranes required relative harsh chemical cleaning
conditions at a pH value of 12. The relative ease of cleaning of
the grafted membranes indicates that the foulants have more or
stronger interactions with the native membrane as compared to the
grafted membranes, again showing that grafting of ceramic NF
membranes diminishes their fouling behavior.
The results of the cleaning experiments also provide an indication
of the excellent stability of the grafting and the strength of
foulant-membrane interactions.
Conclusions
The above results clearly indicate that grafting of NF TiO.sub.2
membranes via reaction of the membrane with phosphonic acids or
organometallic reagents can decrease their fouling tendency. In
particular grafting with methyl groups using the Grignard technique
leads to membranes with an unparalleled low sensitivity to
irreversible fouling.
Cleaning experiments showed that all graftings are stable in basic
media up to pH 10 and allowed for a proper cleaning of the grafted
membranes, thereby fully restoring their water flux and
anti-fouling capacity. All obtained fouling results show that
grafting results in vast fouling resistance, making it very
interesting to enhance the commercial application potential of
ceramic NF membranes for water treatment.
2. Fouling Prevention in Oil/Water Separation
A huge amount of waste water streams exist which are contaminated
with oil. Currently, oil production is one of the biggest sources
of oil-contaminated waste water.
Nevertheless, also several other industrial sectors produce such
effluents.
Open ultrafiltration membranes (having pore sizes from 20 to 200
nm) offer a good separation option for the treatment of
oil-contaminated water. Unfortunately, membrane fouling is a
serious issue.
The present inventors have performed tests to evaluate the
antifouling properties of the membranes described herein, when used
for oil contaminated water treatment. The tests were performed on a
model oil/water emulsion mimicking real oil-contaminated water
resulting from oil production and other oil-containing (waste)
water streams.
For these tests three commercially available TiO.sub.2 membranes
(obtainable from Inopor, Germany) with a pore size of 30 nm were
used. A first TiO.sub.2 membrane was grafted with methyl groups
using Grignard grafting (see section 1.A above) and a second
TiO.sub.2 membrane was grafted with methyl groups using phosphonic
acid grafting (see section 1.A above). The third TiO.sub.2 membrane
was not grafted and was used as a control.
Fouling tests were performed with all three membranes to determine
the irreversible fouling. The fouling tests were similar to the
tests as described above for Example 1 (here performed at 1 bar
instead of at 5 bar), but with the use of different oil/water model
emulsions as foulant solutions.
When comparing the membrane flow at the beginning and the end of
the tests, the ungrafted TiO.sub.2 membranes showed a flow
reduction of more than 50% due to irreversible fouling, whereas the
flow reduction for the grafted TiO.sub.2 membranes was less than
10%. This indicates that the grafted membranes are significantly
less sensitive to irreversible fouling.
This example clearly shows that the grafted membranes described
herein also provide antifouling properties when using the membranes
for the treatment of oil contaminated water. The results further
show that the present methods are not limited to porous membranes
having a pore diameter of about 1 nm as described in Example 1, but
are also useful for much opener membranes.
* * * * *